【单选题】
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.
s 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 trip,_________(60) they become calm again when the time of the flight has ended.
Scientists say they are beginning to learn which _______(61) of the brain contain biological clocks.An American researcher, Martin Moorhead, said a small group of cells near the front of the brain _________(62) to control the timing of some of our actions.These __________(63) tell a person when to wake, when to________() and when to seek food.Scientists say there probably are other biological clock cells that__________ (65) other body activities.
第 51 题
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