单选题   Para. 1 ①Rita Gunther McGrath, a Columbia Business School professor, is one of those business travelers who do not care about delays, cancellations or navigating a new location. ②What does concern her is the seeming inability to conquer jet lag, and the accompanying symptoms that leave her groggy, unfocused and feeling, she says, 'like a dishrag.'
    Para. 2 'Jet lag has always been an issue for me,' says Ms. McGrath, who has been a business traveler for more than two decades and has dealt with itineraries that take her from New York to New Zealand to Helsinki all within a matter of days.
    Para. 3 She has scoured the Internet for 'jet lag cures,' and has tried preventing or dealing with the misery by avoiding alcohol, limiting light exposure or blasting her body with sunlight and 'doing just about anything and everything that experts tell you to do,' Ms. McGrath said.
    Para. 4 ①'Jet lag is not conducive to the corporate environment,' she said. ②'There has to be some kind of help that actually works for those of us that travel a lot, but I sure can't find it.'
    Para. 5 Although science is closer to understanding the basic biological mechanisms that make many travelers feel so miserable when crossing time zones, research has revealed that, at least for now, there is no one-size-fits-all recommendation for preventing or dealing with the angst of jet lag.
    Para. 6 ①Recommendations to beat jet lag include adjusting sleep schedules, short-term use of medications to sleep or stay awake, melatonin supplements and light exposure timing, among others, said Col. Ian Wedmore, an emergency medicine specialist for the Army. ②These work for many people, 'but not all,' said Dr. Wedmore, who practices at Madigan Army Medical Center in Tacoma, Wash.
    Para. 7 Doctors do know that heading west is generally easier on the body than traveling east, because it requires a person's internal clock to 'set later, not earlier,' said Dr. Robert Auger, a sleep specialist at the Mayo Clinic in Rochester, Minn.
    Para. 8 But the more time zones crossed, the tougher the jet lag.
    Para. 9 The rule of thumb to get your body clocks back in sync is about one day per time zone change, making it 'very difficult for real road warriors to get acclimated,' Dr. Auger said.
    Para. 10 A common aid is melatonin, which has been studied extensively and for many travelers can help symptoms by getting the body in sync with local time more quickly, said Dr. Wedmore.
    Para. 11 Although it's not a miracle cure, 'some studies do show it can help on both eastward and westward flights, and it does seem to help a lot of people with jet lag, including me,' he said.
    Para. 12 ①But it hasn't done much for Ms. McGrath. ②So, for now, she's trying to find the positives.
    Para. 13 ①'What we all need to remember is that we are incredibly privileged to be able to cross time zones so rapidly,' she said. ②'Plus, when I get home from a business trip and say something stupid, I just blame the jet lag. ③That's good for about three days.'