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OG18官方指南,建议同学们刷3遍。第一遍做题了解题型和考点,第二遍精刷,第三遍集中解决疑难问题。建议考生第一遍刷题采用官方正版纸质书籍,若遇到疑难问题,欢迎在此专区查阅解析,提供解析,参与题目讨论,与所有考生一起解决疑难问题。
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该题平均耗时:4m29s,平均正确率:70.7%

建议使用官方纸质指南,查看对照完整题目

In the Sonoran Desert of northwestern Mexico and southern Arizona, the flowers of several species of columnar cacti-cardon, saguaro, and organ pipe-were once exclusively pollinated at night by nectar-feeding bats, as their close relatives in arid tropical regions of southern Mexico still are. In these tropical regions, diurnal (daytime) visitors to columnar cactus flowers are ineffective pollinators because, by sunrise, the flowers' stigmas become unreceptive or the flowers close. Yet the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise, allowing pollination by such diurnal visitors as bees and birds. Why have these cacti expanded their range of pollinators by remaining open and receptive in daylight?

This development at the northernmost range of columnar cacti may be due to a yearly variation in the abundance-and hence the reliability-of migratory nectar-feeding bats. Pollinators can be unreliable for several reasons. They can be dietary generalists whose fidelity to a particular species depends on the availability of alternative food sources. Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species. Finally, they may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.

Recent data reveals that during spring in the Sonoran Desert, the nectar-feeding bats are specialists feeding on cardon, saguaro, and organpipe flowers.However, whereas cactus-flower abundance tends to be high during spring, bat population densities tend to be low except near maternity roosts. Moreover, in spring, diurnal cactus-pollinating birds are significantly more abundant in this region than are the nocturnal bats. Thus, with bats being unreliable cactus-flower pollinators, and daytime pollinators more abundant and therefore more reliable, selection favors the cactus flowers with traits that increase their range of pollinators. While data suggest that population densities of nectar-feeding bats are also low in tropical areas of southern Mexico, where bats are the exclusive pollinators of many species of columnar cacti, cactus-flower density and bat population density appear to be much more evenly balanced there:compared with the Sonoran Deses cardon and saguaro, columnar cacti in southern Mexico produce far fewer flowers per night. Accordingly, despite their low population density, bats are able to pollinate nearly 100 percent of the available flowers.

【OG20-P426-525题】

The primary purpose of the passage is to

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  • 分析B选项
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  • 分析C选项
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  • 分析D选项
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  • 分析E选项
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该题目由网友LyKtQL提供。更多GMAT题目请
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当前版本由 百香果蜂蜜茶 更新于2017-08-10 15:32:22 感谢由 百香果蜂蜜茶 对此题目的解答所做出的贡献。

A选项(错)通读全文便可以发现 这篇文章并不是在比较两种cacti的适应能力

B选项(错)蝙蝠的数量稀少仅仅是用来解释为什么在 Sonoran Desert’s columnar cacti的适应能力强,而没有说明蝙蝠数量少的原因

C选项(对)通篇文章都是在说为什么这种cacti在白天也可以pollinated

D选项(错)注意关键字眼 “challenge” 文章是在解释为什么白天也授粉的原因,并非chalenge 这个原因

E选项(错)也很扯啦,并没有对比两个时间段授粉的效率啦


题目讨论 3条评论)

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    一定要上750

    文章结构
    第一层
    SD的花白天也开 VS SM的花只夜晚开 ,问Why?
    第二层
    SD的pollinator不可靠:generalist不只吃SD的这种花
                                          specialist自己的数量波动,不稳定
                                          specialist自己数量一直低
    第三层
    SD 夜晚也有bat吃,但是SD多,bat少,但是白天birds多(bird也pollinate)
    所以SD白天也开花(迎合bird)
    SM的bat也少,但是花也少,所以二者even,全可以pollinate,就不需要白天开花了
    
    文章主要搞清楚两个花的品种,名字贼长,种类贼多,还不如用地名来进行分类,就可以确定出SD白天也pollinate,而SM的只夜晚pollinate
    0 0 回复 2020-04-08 16:24:00
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    Leonyyyyyyyyyyy

    1.两个沙漠区域的花都大部分仅仅只在晚上由一种蝙蝠授粉,因为白天效率太低太差了。 但是,S区域的花进化出了在白天开的能力, 这是为啥?
    2.可能是bat的原因, 不靠谱原因有以下几个:;
    3.不靠谱原因后续:
    0 0 回复 2019-01-23 00:08:38
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    百香果蜂蜜茶

    A选项(错)通读全文便可以发现 这篇文章并不是在比较两种cacti的适应能力
    B选项(错)蝙蝠的数量稀少仅仅是用来解释为什么在 Sonoran Desert’s columnar cacti的适应能力强,而没有说明蝙蝠数量少的原因
    C选项(对)通篇文章都是在说为什么这种cacti在白天也可以pollinated
    D选项(错)注意关键字眼 “challenge” 文章是在解释为什么白天也授粉的原因,并非chalenge 这个原因
    E选项(错)也很扯啦,并没有对比两个时间段授粉的效率啦
    0 0 回复 2017-08-09 13:48:25
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