填空题

Questions 47 to 51 are based on the following passage.
With the global economy now taking more executives to far-away places like Beijing and Mumbai, jet lag is becoming a bigger problem, leading sleep researchers to work harder than ever to find suitable remedies.
Trips to the other side of the globe make adjusting a traveler’s body clock a more lasting process. Jet lag experts say they believe it takes one day for each time zone away from home, up to a maximum of six or seven days, to get fully in sync (同步) with local time.
There is no easy remedy. One problem in developing solutions is all the variation in travelers’ ability to handle jet lag. Sleep researchers have found that people who have dealt with sleep loss over long periods—on night shifts, for example can tolerate jet lag better than most. And older travelers also tend to get harder hit than the young by jet lag. About eight million corporate travelers made overseas trips last year, most of whom were flying to Europe or the Pacific area, throwing their body clocks off kilter and the effects are considered greater going East than West.
Using a combination of nap and caffeine (咖啡因) is better than using them separately, if you can believe it. It takes 15 to 30 minutes for caffeine to kick in. So you do the two together. All it takes is a cup of coffee--not even a pill. By the time the caffeine is working, your nap is over.
Sleep experts are also working with professional and amateur athletes who, of course, change time zones to play "away" games or perform at international meets. A proper amount of sleep can boost an athlete’s performance as much as 30 percent. They are broadening their research to include the disconnection between flying fatigue and work patterns called "journey management". For example, when companies bring together staff from all over the world for a project, the experts will help coordinate the trips to help make sure everyone is productive when they arrive.
Jet lag may be largely sleep interruption, but it’s really a complex mixture of being out of sync with your normal pattern of behavior, plus other factors, even including airline food. If you’re going to be abroad for only a few days. why fool around with so many solutions If you keep resetting your body clock, you’ll end up confusing your feelings.
How long will it take to adjust to the local time if you leave China for America