阅读理解。 We have known for a long time that flowers of different plants open and close at different time of day. This is so familiar that there seems to be no need to ask the reason for it. Yet no one really understands why flowers open and close like this at particular times. The process (过程) is not as simple as we might think, as recent experiments have shown. In one study, flowers were kept in constant (连续的) darkness. We might expect that the flowers, without any information about the time of day, did not open as they normally do. In fact, they continued to open at their usual time. This suggests that they have some mysterious (神秘的) way of knowing the time. Their sense of time does not depend on information from the outside world; it is, so to speak, inside them, a kind of 'inner clock'. This discovery (发现) may not seem to be very important. However, it was later found that not just plants but also animals -including man -have this 'inner clock' which controls the working of their bodies and influences (影响) their activities. Men, then, are also influenced by this mysterious power. 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 matter very much because people lived in natural condition. In the modern 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 useful, then, to know more about the 'inner clock'. Such ordinary things as flowers might help us understand more about ourselves. 1. A recent experiment showed that _______. [     ] A. different flowers open and close at different times of day B. for their opening and closing, flowers do not need information from the outside world C. flowers are influenced by weak light even when they are in a dark room D. flowers can be used for telling the time 2. The 'inner clock' _______. [     ] A. is an unimportant discovery B. is only found in animals C. has not been understood by far D. has an effect on human life 3. Further study of the 'inner clock' will be useful because . [     ] 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 _______. [     ] 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. [     ] 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