完形填空。
We have known for a long time that flowers of different plants open and close at different times
of  day.This is so__1__that there seems to be no need to ask the reason for it. Yet no one__2__
understands why flowers open and close like this at particular times. The process is not as__3__
as we might think,as recent experiments have shown. In one study, flowers were kept in constant
__4__.We might expect that the flowers, without any information about the time of day, did not
open as they __5_ do. As a matter of fact, they __6__to open at their usual time. This suggests
that they have some mysterious(神秘的) way of knowing the __7__.Their sense of time does not
__8__information from the outside world; it is, so to speak, inside them, a kind of "inner clock".
This __9__ may not seem to be very important. However, it was later found that not just plants
but also __10__, including man, have this "inner clock" which __11__the working of their bodies
and influences their activities. Men, then, are also influenced by this mysterious __12__.Whether
we wish it or not, it affects such things in our life as our need for sleep, our need for food.
In the past, this did not really__13__ because people lived in natural condition. Inthe__14__
world, things are different; now there are spacemen, airplane pilots and, in ordinary life, a lot of
people who have to work at night. It would be very __15_  ,then, to know more about the "inner
clock". Such things as flowers might help us understand more about ourselves.
(     )1. A. familiar
(     )2. A. partly
(     )3. A. complex
(     )4. A. quietness
(     )5. A. finally
(     )6. A. refused
(     )7. A. time
(     )8. A. deal with
(     )9. A. discovery
(     )10.A. beasts
(     )11.A. controls
(     )12.A. world
(     )13.A. happen
(     )14.A. ancient
(     )15.A. hard

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