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  3. The plant called the scarlet gilia can have either red or white flowers. It had long been thought that hummingbirds, which forag

The plant called the scarlet gilia can have either red or white flowers. It had long been thought that hummingbirds, which forag

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问题 The plant called the scarlet gilia can have either red or white flowers. It had long been thought that hummingbirds, which forage by day, pollinate its red flowers and that hawkmoths, which forage at night, pollinate its white flowers. To try to show that this pattern of pollination by colors exists, scientists recently covered some scarlet gilia flowers only at night and others only by day: plants with red flowers covered at night became pollinated; plants with white flowers covered by day became pollinated.
Which of the following, if true, would be additional evidence to suggest that hummingbirds are attracted to the red flowers and hawkmoths to the white flowers of the scarlet gilia?
选项 A、Uncovered scarlet gilia flowers, whether red or white, became pollinated at approximately equal rates.
B、Some red flowers of the scarlet gilia that remained uncovered at all times never became pollinated.
C、White flowers of the scarlet gilia that were covered at night became pollinated with greater frequency than white flowers of the scarlet gilia that were left uncovered.
D、Scarlet gilia plants with red flowers covered by day and scarlet gilia plants with white flowers covered at night remained unpollinated.
E、In late August, when most of the hummingbirds had migrated but hawkmoths were still plentiful, red scarlet gilia plants produced fruit more frequently than they had earlier in the season.
答案D
解析 The results reported in the last sentence of the passage suggest that hummingbirds do pollinate red-flowered plants and that hawkmoths do pollinate white-flowered plants. But to prove that they are attracted preferentially to those colors requires knowing whether they also pollinate flowers of the other color that are uncovered during their respective foraging hours—white flowers uncovered during hummingbirds’ daytime hours, and red flowers uncovered during hawkmoths’ nocturnal hours. Choice D states that such plants remain unpollinated, so it is the correct answer. Of the other options, both Choices C and E could suggest the opposite of what is required, so they are incorrect. Choice A is incorrect because the comparative frequency at which uncovered gilia flowers are pollinated has no bearing on the argument. Likewise, the presence of some quantity of unpollinated flowers of either color does not affect the argument, so Choice B is also incorrect.
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