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A. it might help us in some way
B. we do not yet understand plants and animals well enough
C. the number of spacemen and airplane pilots is fast increasing
D. we should try to live more naturally than we do now
4. Kept in constant darkness, flowers _______.
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A. will not open or close as usua
B. will not open any longer
C. will open as they do in natural conditions
D. will always remain in full blossom (开花)
5. ______ have a mysterious power of knowing time without information from the outside world.
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A. Animals including man as well as plants
B. All living things except man
C. Flowers are the only things in the world that
D. Neither animals nor plants