题目内容
（请给出正确答案）
Experiments showed that ______.
A．birds are likely to get lost if there aren't man-made stars.
B．day-flying birds depend on the sun while night-flying birds depend on the stars
C．birds depend on the sun to guide them
D．birds depend on the stars to guide them
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更多“Experiments showed that ______…”相关的问题
Experiments showed that nondrinkers had______.
A．higher blood pressure
B．lower blood pressure
C．larger amounts of' good cholesterol
D．smaller amounts of good cholesterol
听力原文： Why don't birds got lost on their long migratory flights？ 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 mainly by night？ Tests with artificial stars have proved conclusively that certain night-flying birds are able to follow the stars in their long-distance flights.
One such bird—a warbler—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 at migration time. The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the make-believe stars caused a change in the direction of his flight.
Scientists think that warblers, when flying in daylight, use the sun for guidance. But the stars are apparently their principal means of navigation. What do they do when the stars are hidden by clouds？ Apparently, they find their way by such landmarks as mountain ranges, coast lines, and rivet courses. But when it's too dark to see these, the warblers circle helplessly, unable to get their bearings.
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A．Birds have to be taught to navigate.
B．A bird that has been caged will not.
C．Some birds cannot fly at night.
D．Some birds seem instinctively to follow the stars when flying at night.
What didn\'t Mr. Cousins do in his experiments with laughter？
A．Watch funny TV shows.
B．Read funny books.
C．Take medicine.
D．Sleep whenever he felt tired.
What didn't Mr. Cousins do in his experiments with laughter？
A．Watch funny TV shows.
B．Read funny books.
C．Sleep whenever he felt tired.
D．Take medicine.
What didn’t Mr．Cousins do in his experiments With laughter
A．Watch funny TV shows．
B．Read funny books．
C．Sleep whenever he felt tired．
D．Take medicine．
What didn\'t Mr. Cousins do in his experiments with laughter？
A．Watch funny TV shows.
B．Read funny books.
C．Sleep whenever he felt tired.
D．Take medicine.
What didn't Mr. Cousins do in his experiments with laughter？
A． Watch funny TV shows.
B． Read funny books.
C． Sleep whenever he felt tired.
D． Take medicine.
In the author's opinion, why do more people in Britain oppose animal experiments？
A．Because they are kinder than those in the United States.
B．Because they don't know the benefits resulting from animal tests.
C．Because most of the medicines don't need animal experiments to work well.
D．Because some scientists use rare species for their medical experimentation.
What didn’t Mr．Cousins do in his experiments with laughter7
A．Watch funny TV shows．
B．Read funny books．
C．Sleep whenever he felt tired．
D．Take medicine．
