Jet lag， caused by traveling between time zones， is becoming a common problem for frequent travelers： for 49 percent it is only a nuisance and for 45 percent it is a real problem. It is caused by disruption（混亂）to the internal biological clock， and may lead to digestive problems， tiredness， and sleep disruption.

　　Generally speaking， our biological clock is slightly disturbed if we just move into the next time zone， but jet lag becomes a problem once we have passed through three or four time zones. The body takes about one day to get over each hour of time difference. But the seriousness of jet lag problems also depends on our direction of travel. If we go north or south， we won’t notice any difference， because there is usually no time zone change. However if we travel west we will be in advance of ourselves as far as our internal clock is concerned， and problems may arise. A west-to-east journey， on the other hand， makes us late compared to the local time. It often demands even greater effort in adjustment since we are not quick enough to catch up with the new time schedule. Therefore， a trip from New York to Los Angeles often causes fewer problems than a Los Angeles-New York trip.

45. A traveler who suffers from jet lag has problems in ____________.

　　A. adjusting his biological clock

　　B. knowing the direction of a jet

　　C. knowing the distance of his flight

　　D. getting used to the weather of a new place

46. If one travels across three time zones， he needs about ____________ hours to get over his jet lag problem.

　　A. 24 B.                 36                               C. 48                     D. 72

47. A person may suffer the most serious case of jet lag when he takes a ____________ journey.

　　A. east-to-west B. west-to-east C. north-to-south D. south-to-north

48. The main purpose of the passage is to ____________.

       A. explain the cause of jet lag problems

　　B. teach us how to avoid jet lag problems

　　C. explain the differences between time zones

　　D. show the ways to lessen the degree of jet lag problems

Jet lag, caused by traveling between time zones，is becoming a common problem for frequent travelers：for 49 percent it is only a nuisance and for 45 percent it is a real problem. It is caused by disruption（混亂）to the internal biological clock，and may lead to digestive problems,tiredness,and sleep disruption.

　　Generally speaking，our biological clock is slightly disturbed if we just move into the next time zone，but jet lag becomes a problem once we have passed through three or four time zones. The body takes about one day to get over each hour of time difference. But the seriousness of jet lag problems also depends on our direction of travel. If we go north or south，we won’t notice any difference，because there is

usually no time zone change. However if we travel west we will be in advance of ourselves as far as our internal clock is concerned，and problems may arise. A

west-to-east journey，on the other hand，makes us late compared to the local time. It often demands even greater effort in adjustment since we are not quick enough to catch up with the new time schedule. Therefore，a trip from New York to Los Angeles often causes fewer problems than a Los Angeles-New York trip.

1. A traveler who suffers from jet lag has problems in ____________.

A. adjusting his biological clock

B. knowing the direction of a jet

C. knowing the distance of his flight

D. getting used to the weather of a new place

2. If one travels across three time zones， he needs about ____________ hours to get over his jet lag problem.

A. 24　　　　　 B. 36　　　 C.48　　　　 D. 72

3. A person may suffer the most serious case of jet lag when he takes a ____________ journey.

A. east-to-west　 B. west-to-east　 C. north-to-south D. south-to-north

4. The main purpose of the passage is to ____________.

A. explain the cause of jet lag problems

B. teach us how to avoid jet lag problems

C. explain the differences between time zones

D. show the ways to lessen the degree of jet lag problems

5. What does affect the biological clock?

A. healthy body　 B. direction　　 C. time zones　 D. sleeping