单选题
Most people who travel long distance complain of jetlag. Jetlag makes business travelers less productive and more prone【C1】______making mistakes. It is actually caused【C2】______of your " body clock"—a small cluster of brain cells that controls the timing of biological【C3】______. The body clock is designed for a【C4】______rhythm of daylight and darkness, so that it is thrown out of balance when it【C5】______daylight and darkness at the " wrong" times in a new time zone. The symptoms of jetlag often persist for days【C6】______the internal body clock slowly adjusts to the new time zone. Now a new anti-jetlag system is【C7】______that is based on proven tentative pioneering scientific research. Dr. Martin Ede had【C8】______a practical strategy to adjust the body clock much sooner to the new time zone【C9】______controlled exposure to bright light. The time zone shift is easy to accomplish and eliminates【C10】______of the discomfort of jetlag. A successful time zone shift depends on knowing the exact time to either【C11】______or avoid bright light. Exposure to light at the wrong time can actually make jetlag worse . The proper schedule【C12】______light exposure depends a great deal on specific travel plans. Data on a specific flight itinerary and the individual" s sleep【C13】______are used to Produce a Trip Guide with【C14】______on exactly when to be exposed to bright light. When the Trip Guide calls for bright light you should spend time outdoors if possible. If it is dark outside, or the weather is bad, 【C15】______you are on an airplane, you can use a special light device to provide the necessary light stimulus for a range of activities such as reading, watching TV or working.