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  3. The curse of jet lag has struck most international travelers at one time or another -- and anyone lucky enough to have avoided i

The curse of jet lag has struck most international travelers at one time or another -- and anyone lucky enough to have avoided i

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问题     The curse of jet lag has struck most international travelers at one time or another -- and anyone lucky enough to have avoided it will surely have suffered the equally unpleasant sleep-deprivation involved in an early-morning start. Nor, as shift workers know too, is it possible to escape by going to bed earlier the previous evening, and thus putting sleep in the bank. Sleepiness is controlled by the body’s internal biological clock, so an earlier bedtime just means several wakeful hours staring in frustration at a darkened ceiling.
    For years, some travelers and shift workers have sworn by melatonin (褪黑素). This is a hormone that regulates the biological clock. It is made in the brain by a structure called the pineal gland (松果体), as darkness sets in after sunset. Light is the one that keeps the biological clock in the same pace with solar time. The clock then tells the brain when to go to sleep. The theory of those who use melatonin is that an external dose of it can reset the clock, and thus cause the "go to sleep" signal to be sent at a more convenient moment~ Melatonin can also increase sleepiness during the day, when the pineal gland is not producing it.
    This has resulted in a growing, and often unregulated, market in melatonin-supplement tablets. The pharmaceutical industry’s response to this seems to be: "If you can’t beat them, join them." A paper in this week’s Lancet, by Shantha Rajaratnam of the Harvard Medical School and his colleagues, reports two trials, funded by drug companies, of tasimelteon, a substance that binds to the same receptors in the brain as melatonin does, and which it is expected will have a similar effect.
    In the course of these trials, more than 400 people had their bedtimes brought forward by five hours in controlled conditions. Half an hour before lights out, a quarter of them were given common drug, while the remaining three-quarters were given varying doses of tasimelteon. Dr. Rajaratnam and his colleagues report that the new drug let people fall asleep faster at the unnaturally early time, and also allowed them to sleep longer than those given the common one.
Going to bed earlier, you may be frustrated by body’s internal biological clock in keeping you ______.
选项
答案wakeful for several hours
解析 由题干中的Going to bed earlier和body’s internal biological clock，可将本题出处定位到第一段最后一句。该句说，睡眠由身体内的生物钟控制，早睡只会意味着几小时睡不着(several wakeful hours)。题干中的be frustrated对应原文中的in frustration。空白处应填入keep的宾语补足语，意思是“使某人保持某一状态”，将原文中的名词短语转换为形容词短语即为答案。
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