Most people who travel long distance complain of jet-lag. Jet-lag 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 jet-lag often persist for days 【27】______ the internal body clock slowly adjusts to the new time zone.

Now a new anti-jet-lag system is 【28】______ that is based on proven 【29】______ pioneering scientific research. Dr. Martin Moore-Ede had 【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 jet-lag.

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 jet-lag worse. The proper schedule 【34】______ light exposure depends a great deal on 【35】______ travel plans.

Data on a specific flight itinerary 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 aeroplane, 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．from

B．of

C．for

D．to