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 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 _________(64) and when to seek food. Scientists say there probably are other biological clock cells that __________(65) other body activities.
51 A says B asks C talks D tells
52 A reach B leave C escape D enter
53 A affect B adopt C avoid D express
54 A time B value C amount D number
55 A days B months C minutes D weeks
56 A shape B type C form D color
57 A physical B biological C mental D portable
58 A operation B flight C movement D transportation
59 A derived B prevented C originated D protected
60 A but B unless C therefore D if
61 A parts B ideas C sorts D images
62 A tries B likes C seems D wants
63 A functions B places C actions D cells
64 A lie B sleep C stand D walk
65 A build B demand C reflect D control
答案：51.D 52.B 53.A 54.D 55.A 56.D 57.B 58.B 59.B 60.A 61.A 62.C 63.D 64.B 65.D
