在射击瞄准时，有一个要领叫做“三点一直线”，是利用了光沿 ___________
题型：填空题
问题：
在射击瞄准时，有一个要领叫做“三点一直线”，是利用了光沿 ___________原理。
题型：填空题
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| 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. In  the 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. | ||||
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