A、About 13%. B、About 15%. C、About 30%. D、About 50%. C

With the global economy now taking more executives to far-away places like Beijing and Tokyo, jet lag is becoming a bigger problem. Sleep researchers are working 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 harmony with local time. Using a combination of naps and caffeine is better than using them separately, if you can believe it. It takes 15 to 30 minutes for caffeine to kick in. So you may do the two together. All it takes is a cup of coffee. By the time the caffeine is working, your nap is over. Sleep experts are also working with professional and amateur athletes who perform at international meets. A proper amount of sleep can improve an athlete’s performance as much as 30%. But there is no easy remedy. The problem lies in the differences in travelers’ ability to handle jet lag. Sleep researchers have found that people who have dealt with sleep loss over long periods can tolerate jet lag better than most. And older travelers also tend to get hit harder than the young by jet lag.
16.  What should we do to deal with jet lag according to the passage?      
17.  How much improvement can a proper amount of sleep make to the athletes’ performance?      
18.  Which of the following group can tolerate jet lag better than others?