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 by【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【C6】______of jetlag often persist for days【C7】______the internal body clock slowly adjusts to the new time zone. Now a new anti-jetlag system is【C8】______that is based on proven【C9】______pioneering scientific research. Dr. Martin Moore Ede had【C10】______a practical strategy to adjust the body clock much sooner to the new time zone 【C11】______controlled exposure to bright light. The time zone shift is easy to accomplish and eliminates【C12】______of the discomfort of jetlag. A successful time zone shift depends on knowing the exact times to either【C13】______or avoid bright light. Exposure to light at the wrong time can actually make jetlag worse. The proper schedule【C14】______light exposure depends a great deal on【C15】______travel plans. Data on a specific flight itinerary and the individual"s sleep【C16】______are used to produce a Trip Guide with【C17】______on exactly when to be exposed to bright light. When the Trip Guide calls【C18】______bright light you should spend time outdoors if possible. If it is dark outside, or the weather is bad, 【C19】______you are on an aeroplane, you can use a special light device to provide the necessary light【C20】______ for a range of activities such as reading, watching TV or working.