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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 many ye

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

admin2013-01-22  29
问题     Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for many years. Now they’re beginning to fill in the blanks.
    Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by 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 (鸽子) had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed 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 principal means of navigation (航行) only. When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it’s too dark to see these, 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 (n.窝)
C、doves under the natural sky
D、other birds in general
答案C
解析 文中第三段第四句说：“这只鸽子也像它的outdoor cousins一样朝着一个方向飞。”从第三段中我们得知，这只鸽子是一直生活在笼中且从未在大自然的天空下飞翔过的鸽子。但它同样显示出能以星星作为导航的能力。由此我们可以推断出，与这只鸽子相对比的鸽子一定是在大自然的天空下飞行的鸽子。因此选项C正确。其余三个选项均与文中内容不符。
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