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 disruption of your "body clock"—a small cluster of brain cells that controls the timing of biological 【C2】______. The body clock is designed for a regular rhythm of daylight and darkness, so that it is thrown out of balance when it 【C3】______daylight and darkness at the "wrong" times in a new time zone. The 【C4】______of jetlag of ten persist for days while the internal body clock slowly adjusts to the new time zone. Now a new anti-jetlag system is【C5】______that is based on proven【C6】______pioneering scientific research. Dr. Martin Mooreede had devised a practical strategy to adjust the body clock much sooner to the new time zone【C7】______controlled exposure to bright light. The time zone shift is easy to accomplish and eliminates 【C8】______of the discomfort of jetlag.A successful time zone shift depends on knowing the exact times to either 【C9】______or avoid bright light. Exposure to light at the wrong time can actually make jetlag worse. The proper schedule for light exposure depends a great deal【C10】______specific travel plans.