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  3. Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for a long

Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for a long

admin2015-04-17  54
问题     Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for a long time. Now they’ re starting to fill in the blanks.
    Not long ago, experiments showed that birds use the sun to guide them during daylight hours. How do birds fly at night? Tests with artificial stars have proved that certain night-flying birds are able to follow the stars in their long-distance flights.
    A dove had spent its lifetime in a cage and had never flown under a natural sky. But it had an inborn ability to use the stars for guidance.  The bird’ s cage was placed under an artificial star-filled sky. The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the artificial stars caused a change in the direction of his flight.
    But the stars are apparently their main means of navigation. When the stars are hidden by clouds, they apparently find their way by such landmarks as river courses, mountain ranges, coast lines. But when it’ s too dark to see these things, the doves circle helplessly, unable to find their way.
By "his outdoor cousins" the author means______.
选项 A、other experimenters
B、the other doves of the same brood
C、doves under the natural sky
D、other birds in general
答案C
解析 A项“其他实验者”；B项“其他同一窝的鸽子”；C项“在自然天空下飞行的鸽子”；D项“其他鸟类”。根据题意，C为正确答案。
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