共用题干A Biological Clock<br>Every living thing has what scientists call a biological clock that controls behavior. The bio- logical clock tells______(51)when to form flowers and when the flowers should open. It tells ______(52)when to leave the protective cocoons and fly away,and it tells animals and human beings when to eat,sleep and wake.<br>Events outside the plant and anima______(53)the actions of some biological clocks.Sci- entists recently found,for example,that a tiny animal changes the color of its fur______(54) the number of hours of daylight.In the short______(55)of winter,its fur becomes white.The fur becomes gray brown in color in the longer hours of daylight in summer.<br>Inner signals control other biological clocks.German scientists found that some kind of internal clock seems to order birds to begin their long migration______(56)twice each year. Birds ______(57)flying become restless when it is time for the trip,______(58)they become calm again when the time of the flight has ended.<br>Scientists say they are beginning to learn which______(59)of the brain contain biologica] clocks.An American researcher,Martin Moorhead,said a small group of cells near the front of the brain______（60)to control the timing of some of our actions.These______(61)tell a person when to______(62),when to sleep and when to seek food.Scientists say there proba- bly are other biological clock cells that control other body activities.<br>Dr Moorhead is studying______(63)our biological clocks affect the way we do our work .For example,most of us have great difficulty if we must often change to different work hours.<br>______(64)can take many days for a human body to accept the major change in work hours .Dr. Moorhead said industrial officials should have a better understanding of biological clocks and how they affect workers.He said______(65)understanding could cut sickness and accidents at work and would help increase a factory's production.60._________