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题库总题数: 9689
做题总人数: 140128
平均每天做题人数: 2373
  • 2018年6月出版,OG19新题即OG2019综合册里与OG18相比新增的题目。此内容做为官方题源可以帮助大家更好的需要了解考点,了解考试趋势和考官思维。OG建议大家刷3遍,第一遍刷纸质,第二遍计时精刷,第三遍刷错题。做完后记得及时分析总结。

    142
    题目总数

    15706
    做题总人数

    78.6%
    平均准确率

    • 【阅读RC】-18437 -搞定GMAT阅读

      It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discovered that the production and release in brain neurons of the neurotransmitter serotonin (neurotransmitters are compounds that neurons use to transmit signals to other cells) depend directly on the food that the body processes. Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryptophan increases. In later studies we found that injecting insulin into a rat’s bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood tryptophan level and the concentrations of tryptophan and of serotonin in the brain increased after the meal. Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein is in a meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and released.

      来源:搞定GMAT阅读 9人已做 其他难度 0%正确率

    • 【阅读RC】-18436 -搞定GMAT阅读

      It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discovered that the production and release in brain neurons of the neurotransmitter serotonin (neurotransmitters are compounds that neurons use to transmit signals to other cells) depend directly on the food that the body processes. Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryptophan increases. In later studies we found that injecting insulin into a rat’s bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood tryptophan level and the concentrations of tryptophan and of serotonin in the brain increased after the meal. Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein is in a meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and released.

      来源:搞定GMAT阅读 9人已做 其他难度 100%正确率

    • 【阅读RC】-18435 -搞定GMAT阅读

      It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discovered that the production and release in brain neurons of the neurotransmitter serotonin (neurotransmitters are compounds that neurons use to transmit signals to other cells) depend directly on the food that the body processes. Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryptophan increases. In later studies we found that injecting insulin into a rat’s bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood tryptophan level and the concentrations of tryptophan and of serotonin in the brain increased after the meal. Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein is in a meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and released.

      来源:搞定GMAT阅读 9人已做 其他难度 88.9%正确率

    • 【阅读RC】-18434 -搞定GMAT阅读

      More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect non-target species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

      来源:搞定GMAT阅读 4人已做 其他难度 25%正确率

    • 【阅读RC】-18433 -搞定GMAT阅读

      More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect non-target species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

      来源:搞定GMAT阅读 4人已做 其他难度 0%正确率

    • 【阅读RC】-18432 -搞定GMAT阅读

      More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect non-target species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

      来源:搞定GMAT阅读 4人已做 其他难度 75%正确率

    • 【阅读RC】-18431 -搞定GMAT阅读

      More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect non-target species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

      来源:搞定GMAT阅读 6人已做 其他难度 50%正确率

    • 【阅读RC】-18430 -搞定GMAT阅读

      More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect non-target species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

      来源:搞定GMAT阅读 8人已做 其他难度 37.5%正确率

    • 【阅读RC】-18429 -搞定GMAT阅读

      More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect non-target species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways, so that it can feed on or otherwise harm new hosts.

      来源:搞定GMAT阅读 6人已做 其他难度 83.3%正确率

    • 【阅读RC】-18428 -搞定GMAT阅读

      Quantum theory, although of tremendous scientific value, has nevertheless prompted debate among physicists. The debate arose because quantum theory addresses the peculiar properties of minute objects such as photons and electrons. While one type of experiment shows that these objects behave like particles, with well-defined trajectories through space, another demonstrates that, on the contrary, they behave waves, their peaks and troughs producing characteristic "interference" effects. However, scientists have failed to devise an experiment to demonstrate both behaviors simultaneously. In the 1920s, two alternate interpretations of quantum theory attempted to resolve this apparently contradictory wave-particle duality. Physicist Niels Bohr argued that wave-particle properties are not contradictory, but complementary. Contrary to our intuition that an object continues to exist in some determined form even though we cannot perceive it, he concluded that the physical of a quantum object is actually undetermined before the object is observed via experiment. Physicist Werner Heisenberg's "uncertainty principle," by contrast, postulated that we cannot precisely determine two complementary properties, such as position and momentum, of a quantum object simultaneously: if we measure an object's position with absolute certainty, then there is an infinite uncertainty in its momentum, and vice versa. He concluded that although we are limited in our ability to measure objects at the atomic and subatomic levels, their position and momentum are nonetheless defined all along.

      来源:搞定GMAT阅读 4人已做 其他难度 75%正确率

热门讨论
  • 【数据充分DS】

    【OG20-P290-424题】The only articles of clothing in a certain closet are shirts, dresses, and jackets. The ratio of the number of shirts to the number of dresses to the number of jackets in the closet is 9:4:5, respectively. If there are more than 7 dresses in the closet, what is the total number of articles of clothing in the closet?(1) The total number of shirts and jackets in the closet is less than 30.(2) The total number of shirts and dresses in the closet is 26.

  • 【逻辑CR】

    Sasha: It must be healthy to follow a diet high in animal proteins and fats. Human beings  undoubtedly evolved to thrive on such a diet, since our prehistoric ancestors ate large amounts  of meat. Jamal: But our ancestors also exerted themselves intensely in order to obtain this food, whereas  most human beings today are much less physically active. Jamal responds to Sasha by doing which of the following?

  • 【数据充分DS】

    【OG20-P289-410题】If r and s are positive integers, can the fraction r/s be expressed as a decimal with only a finite number of nonzero digits?(1) s is a factor of 100.(2) r is a factor of 100.

  • 【问题求解PS】

    【OG20-P181-228题】How many of the integers that satisfy the inequality (x+2)(x+3)x−2 ≥0   are less than 5?

  • 【数据充分DS】

    If ab ≠ 0 and points (-a, b) and (-b, a) are in the same quadrant of the xy-plane, is point (-x, y) in this same quadrant?(1) xy > 0(2) ax > 0

  • 【问题求解PS】

    【OG18-P162-111题】At a certain instant in time, the number of cars, N, traveling on a portion of a certain highway can be estimated by the formula N= 20Ld600+s2 where L is the number of lanes in the same direction, d is the length of the portion of the highway, in feet, and s is the average speed of the cars, in miles per hour. Based on the formula, what is the estimated number of cars traveling on a 1/2 mile portion of the Highway if the highway has 2 lanes in the same direction and the average speed of the cars is 40 miles per hour? (5,280 feet =1mile)

  • 【句子改错SC】

    Since the 1930s aircraft manufacturers have tried to build airplanes with frictionless wings, shaped so smoothly and perfectly that the air passing over them would not become turbulent.

  • 【逻辑CR】

    【OG20-P562-610题】 Arts advocate: Few universities require that students who are specializing in science and technology take many art courses.However, real progress in science and technology requires an element of creativity,which the arts foster. Thus,to help science and  technology  students succeed in  their careers, universities should increase the number of art courses  required for them.Which of the following would,if true, most strengthen the argument above?

  • 【逻辑CR】

    【OG20-P585-685题】A company has developed a new sensing device that, according to the company's claims, detects weak, ultralow-frequency electromagnetic signals associated with a beating heart. These signals, which pass through almost any physical obstruction, are purportedly detected by the device even at significant distances. Therefore, if the company’s claims are true, their device will radically improve emergency teams ability to locate quickly people who are trapped within the wreckage of collapsed buildings. Which of the following, if true, most strengthens the argument?

  • 【句子改错SC】

    【OG20-P814-903题】In the major cities of industrialized countries at the end of the nineteenth century,important public places such as theaters,restaurants,shops,and banks had installed electric lighting ,but electricity was in less than 1 percent of homes,where lighting was still provided mainly by candles or gas.

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