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OG20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。
阅读RC-15417 (第3/6题) Time Cost00:00
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该题平均耗时:2m31s,平均正确率:51.3%

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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-P427-527题】

According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti

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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hnwaUMbt提供。更多GMAT题目请
暂无雷哥网文字解析
当前版本由 百香果蜂蜜茶 更新于2017-08-10 15:34:04 感谢由 百香果蜂蜜茶 对此题目的解答所做出的贡献。

(A)错, 很明显,在晚上(after sunset)两种cacti都会开花

(B) 错,如文章中提到的一样, 两种cacti都由dietary specialists 授粉

(C)错,跟B 一样, C中描述的性质在这两种cacti都有

(D)错, 在这个地区的cacti 无论在白天还是晚上都会开花

(E)对    请锁定这句话,“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” 我们看出 两种cacti的本质区别是,白天受不受粉


题目讨论 7条评论)

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    风中菜鸟

    对比题,同物种在两个地区的区别。定位在第一段。as和yet都是信号词,原来一样(as),进化以后(yet)不一样了
    0 0 回复 2021-08-24 20:03:49
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    495781n

    B选项在文章哪里提到了呢
    0 0 回复 2021-06-27 15:23:52
  • 用户头像

    Ms Eh

    最后一题居然定位第一段:
    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.
    0 0 回复 2020-12-17 18:33:49
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    你这只猪

    sunrise 和sunst 搞错了,晕死得了
    3 0 回复 2020-07-16 10:05:20
  • 用户头像

    SeanDing

    定位第一句, 抓主干:Sonoran Desert were once exclusively pollinated at night
    southern Mexico still are
    
    第三句: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. 
    
    考点在yet
    0 0 回复 2018-08-02 10:26:02
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    xuannner

    by sunrise, the flowers' stigmas become unreceptive or the flowers close. 这不是就是A选项中没开花嘛  怎么能说两种cacti都会开花呢
    0 0 回复 2017-09-17 14:27:06
    • 评论用户头像

      ramipasu回复xuannner

      a选项说的是sunset,日落之后都开花

      0 0 回复 2017-11-04 15:20:55

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    百香果蜂蜜茶

    (A)错, 很明显,在晚上(after sunset)两种cacti都会开花
     (B) 错,如文章中提到的一样, 两种cacti都由dietary specialists 授粉
    (C)错,跟B 一样, C中描述的性质在这两种cacti都有
    (D)错, 在这个地区的cacti 无论在白天还是晚上都会开花
    (E)对    请锁定这句话,“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” 我们看出 两种cacti的本质区别是,白天受不受粉
    0 0 回复 2017-08-09 14:02:13
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