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In terrestrial environments, gravity places special demands on the cardiovascular systems of animals. Gravitational pressure can cause blood to pool in the lower regions of the body, making it difficult to circulate blood to critical organs such as the brain. Terrestrial snakes, in particular, exhibit adaptations that aid in circulating blood against the force of gravity.
The problem confronting terrestrial snakes is best illustrated by what happens to sea snakes when removed from their supportive medium. Because the vertical pressure gradients within the blood vessels are counteracted by similar pressure gradients in the surrounding water, the distribution of blood throughout the body of sea snakes remains about the same regardless of their orientation in space, provided they remain in the ocean. When removed from the water and tilted at various angles with the head up, however, blood pressure at their midpoint drops significantly, and at brain level falls to zero. That many terrestrial snakes in similar spatial orientations do not experience this kind of circulatory failure suggests that certain adaptations enable them to regulate blood pressure more effectively in those orientations.
One such adaptation is the closer proximity of the terrestrial snake’s heart to its head, which helps to ensure circulation to the brain, regardless of the snake’s orientation in space. The heart of sea snakes can be located near the middle of the body, a position that minimizes the work entailed in circulating blood to both extremities. In arboreal snakes, however, which dwell in trees and often assume a vertical posture, the average distance from the heart to the head can be as little as 15 percent of overall body length. Such a location requires that blood circulated to the tail of the snake travel a greater distance back to the heart, a problem solved by another adaptation. When climbing, arboreal snakes often pause momentarily to wiggle their bodies, causing waves of muscle contraction that advance from the lower torso to the head. By compressing the veins and forcing blood forward, these contractions apparently improve the flow of venous blood returning to the heart.
【OG18-P384-447题】
The author suggests that which of the following is a disadvantage that results from the location of snake’s heart in close proximity to its head?
细节题,定位于第三段,从第三段关于树栖蛇的内容可以推测,心脏离头部越近,心脏到蛇尾的血液循环就越慢
A错误,与调节流向脑部的血液无关
B错误,与orientation的数量无关
C错误,这是第二段的内容,与海蛇心脏与头部的距离无关
D错误,与titled at various angles...无关
E正确。该选项谈及了流向蛇尾的血液循环变得更加费劲
A -- no,心脏离头部近,血流应该更容易;B -- 文中没有说到number of orientation的事情; C -- maybe,但这个更多是说海蛇的,路蛇的话应该是从更上面的部分就decrease了;D-- maybe,但文中没怎么提到过。 E -- 要努力让底部循环上来,文中直白的说过,正确。
A冲突,不是decrease
B冲突,原文regardless
CD定位错
E原文....a problem(≈ disadvantage)...
Such a location requires that blood circulated to the tail of the snake travel a greater distance back to the heart, 从这句话推论
不仅是读懂句子,还要思考背后的意思
disadvantage:定位 Such a location requires that blood circulated to the tail of the snake travel a greater distance back to the heart, a problem solved by another adaptation.
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默默回复默默
看概念就好了
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2018-05-17 03:12:42
默默回复默默
however 后面是重点 , 不过根据 however , 可以辨别出论点的对立
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2018-05-17 03:16:38
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