【广东省东莞市第七中学2015届高三第一次月考】

　　Why don’t birds get lost on their long flights from one place to another?

　　Not long ago, experiments showed that birds rely

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　　the sun to guide them during daylight hours. But what about birds

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　　fly by night? Tests with artificial（人造的）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

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　　(nature) sky. Yet

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　　showed an inborn ability to use the stars for guidance. The bird’s cage

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　　(place) under an artificial star-filled sky. The bird tried to fly in the same direction

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　　(take) by his outdoor cousins. Any change in the position of the make-believe stars caused

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　　change in the direction of his flight.

　　Scientists think that doves, when

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　　(fly) in daylight, use the sun for guidance. But the stars are apparently their principal means of navigation. What do they do

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　　the stars are hidden by clouds?

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　　(obvious), they find their way by such landmarks as mountain ranges, coastlines, and river courses. But when it’s too dark to see these, the doves circle helplessly, unable to get their position.

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