Passage 5
Every living thing has an inner biological clock that controlsbehavior. The clock works all the time； even when there areno outside signs to mark the passing of time. The biological clock tells plantswhen to form flowers and when the flowers should open. It tells insects when toleave the protective cocoon and fly a way. And it tells animals when to eat， sleep andwake. It controls body temperature， the release of somehormones and even dreams. These natural daily events are circadian rhythms.
Man has known about them for thousands of years. But the firstscientific observation of circadian rhythms was not made until 1729. In thatyear French astronomer， Jean-Jacques d“Ortous de Mairan， noted that one of his plants opened it s leaves at the same timeevery morning， and closed them at the same time every night. The plant did thiseven when he kept it in a dark place all the time. Later scientists wonderedabout circadian rhythms in humans. They learned that man”s biologicalclock actually keeps time with a day of a little less than 25 hours instead ofthe 24 hours on a man-made clock. About four years ago an American doctor， EliotWeitzman， established a laboratory to study how our biological clock works.The people in his experiments are shut off from the outside world. They arefree to listen to and live by their circadian rhythms. Dr. Weitzman hopes hisresearch will lead to effective treatments for common sleep problems and sleep disorderscaused by ageing and mental illness. The laboratory is in the MontefloreHospital in New York City. It has two living areas with three small rooms ineach. The windows are covered， so no sunlight o r moonlight comes in. There are no radios or televisionreceivers. There is a control room between the living areas. It containscomputers， one-way cameras and other electronic devices for observing theperson in the living area. The instruments measure heartbeat， bodytemperature， hormones in the blood，other substances in the urine and brain waves during sleep. Adoctor or medical technician is on duty in the control room 24 hours a dayduring an experiment. They do not work the same time each day and are notpermitted to wear watches， so the person in the experiment has no idea what time it is. In thefirst four years of research， Dr Weitzman and his assistant have observed 16 men between the agesof 21 and 80. The men remained in the laboratory for as long as six months.Last month， a science reporter for “The New York Times” newspaper， Dava Sobol， became thefirst woman to take part in the experiment. She entered the laboratory on June13th and stayed for 25 days. Miss Sobol wrote reports about the experimentduring that time， which were published in the newspaper.
1、The biological clock is believed to play an essential role in ____.
A、the regulation of body temperature
B、the secretion of hormones
C、animal reproduction
D、many aspects of plant and animal physiology
2、In his observation， the French scientist noticed that the leaves of a certain plantmaintained its opening-and-closing cycles ____.
A、even when it was kept in a murky place all day
B、even if it was placed in the moonlight
C、even when he was observing it from a dark place
D、even during the night time
3、The sentence “They are free to listen to and live by their circadian rhythms.” （In Paragraph 4） probablymeans ____.
A、They can lead their daily lives according to their biological clocks， withoutreferring to a man-made clock.
B、They can listen to the wonderful rhythms of the biological clock andlive close to them.
C、They can live by regulating their own circadian rhythms.
D、They are free from the annoying rhythms of everyday life.
4、In the experiment conducted by Mr. Weitzman， the doctorwho is on duty does not work the same time each day ____.
A、insgroupsto observe the abnormal behavior of the people at differenttimes
B、so as not to be recognized by the people
C、so as to avoid indicating to the people what time it is when hestarts work
D、so as to leave the people“s circadian rhythmsin disorder
5、Miss Sobol left the laboratory ____.
A、on June 13th
B、on June 25th
C、at the end of June
D、on July 7th
Keys to Passage 5
D A A C D