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第六部分 完形填空 （每题1分，共15分）
阅读下面的短文。短文中有15个空白，在文章的后面，每一个空白都列出了四个备选答案。请根据文章的内容选择合适的词或短语填在空白处。
A Biological Clock
Every living thing has what scientists call a biological clock that controls behavior. The biological clock tells _________when to form flowers and when the flowers should open1. It tells _________ when to leave the protective cocoon and fly away, and it tells animals and human beings when to eat, sleep and wake.
Events outside the plant and anima __________the actions of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur________ the number of hours of daylight . In the short _________ of winter , its fur becomes white. The fur becomes gray brown in color in the longer hours of daylight in summer.
Inner signals control other biological clocks. German scientists found that some kind of internal clock seems to order birds to begin their long migration __________ twice each year. Birds __________ flying become restless when it is time for the trip, ___________ they become calm again when the time of the flight has ended.
Scientists say they are beginning to learn which ____________ of the brain contain biological clocks. An American researcher, Martin Moorhead, said a small group of cells near the front[1] [2] [3] [4] [5] 下一页 |
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