[单项选择]A Special Clock Every living thing has what scientists call a biological clock that controls behavior. The biological clock________(51) plants when to form flowers and when the flowers should open. It tells insects when to __________(52) the protective cocoon (防护卵袋) and fly away, and it tells animals and human beings when to eat, sleep and wake. Events outside the plant and animal__________(53) the actions of some biological clocks . Scientists recently found, for example, that a tiny animal changes the color of its fur because of the __________(54) of hours of daylight. In the short_________(55) of winter, its fur becomes white. The fur becomes gray brown in _________(56) in the longer hours of daylight in summer. Inner signals control other _________(57) clocks. German scientists found that some kind of internal clock seems to order birds to begin their long migration_________(58) twice each year. Birds _________(59) from flying become restless when it is time for the
A. tries
B. likes
C. seems
D. wants

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