Most people who travel long distances complain of jetlag （飞行时差综合症). Jetlag makes bu

Most people who travel long distances complain of jetlag (飞行时差综合症). Jetlag makes business travelers less productive and more prone 【21】______ making mistakes. It is actually caused by 【22】______ of your "body clock"--a small cluster of brain cells that controls the timing of biological 【23】______ The body clock is designed for a 【24】______ rhythm of daylight and darkness, so that it is thrown out of balance when it 【25】______ daylight and darkness at the "wrong" times in a new time zone. The 【26】______ of jetlag often persist for days 【27】______ the internal body clock slowly adjusts to the new time zone. Now a new anti-jetlag system is 【28】______ that is based on proven 【29】______ pioneering scientific research. Dr. Martin Moore-Ede has 【30】______ a practical strategy to adjust the body clock much sooner to the new time zone 【31】______ controlled exposure to bright light. The time zone shift is easy to accomplish and eliminates 【32】______ of the discomfort of jetlag. A successful time zone shift depends on knowing the exact times to either 【33】______ or avoid bright light. Exposure to light at the wrong time can actually make jetlag worse. The proper schedule 【34】______ light exposure depends a great deal on 【35】______ travel plans. Data on a specific flight itinerary (旅行路线) and the individual's sleep 【36】______ are used to produce a Trip Guide with 【37】______ on exactly when to be exposed to bright light. When the Trip Guide calls 【38】______ bright light you should spend time outdoors if possible. If it is dark outside, or the weather is bad, 【39】______ you are on an aero plane, you can use a special light device to provide the necessary light 【40】______ for a range of activities such as reading, watching TV or working.

【21】

A．for

B．from

C．to

D．of