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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

admin2014-10-11  53
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 blares.
   Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that 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. 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. When the stars are hidden by clouds, they apparently 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.
In total darkness, doves ______.
选项 A、use landmarks
B、don’t know which way to fly
C、fly back home
D、wait for the stars to appear
答案B
解析 见本文最后一句：“But when it’s too dark to see these, the doves circle helplessly unable to find their way. ”
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