还没有登录哦！
[Reading Comprehension]
试题详情
文章：
| Line | 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 | |
| (5) | 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 | |
| (10) | 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? | |
| (15) | 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 | |
| (20) | 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 | |
| (25) | 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 | |
| (30) | 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 | |
| (35) | 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 | |
| (40) | 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 | |
| (45) | balanced there: compared with the Sonoran Desert’s |
| 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. |
题目：
The primary purpose of the passage is to
选项:
A、compare the adaptive responses of several species of columnar cacti in the Sonoran Desert with those in the arid tropical regions of southern Mexico
B、discuss some of the possible causes of the relatively low abundance of migratory nectar-feeding bats in the Sonoran Desert
C、provide a possible explanation for a particular evolutionary change in certain species of columnar cacti in the Sonoran Desert
D、present recent findings that challenge a particular theory as to why several species of columnar cacti in the Sonoran Desert have expanded their range of pollinators
E、compare the effectiveness of nocturnal and diurnal pollination for several different species of columnar cacti in the Sonoran Desert
答案:
C
提问：
您好 请问E选项为什么不对呢？
解答：
点赞0
阅读1010
提问：
您好 请问E选项为什么不对呢？
解答：
点赞0
阅读1011
提问：
老师能帮忙分析下这篇文章结构吗，考试时读哪些，我在看这篇文章时感觉没有思路，感觉几乎需要全读。
解答：
点赞0
阅读1339
问个问题
注册太麻烦？点这里查看免费答疑吧！
博币不足
加"GMAT小百科"小智微信
直接送200
