下面文章中有5处需要添加小标题。请从以下选项（A、B、C、D、E和F）中选出符合各段意思的小标题。选项中有一项是多余选项。
A. Kripke’s Research Tool
B. Dangers of Habitual Shortages of Sleep
C. Classification of Sleep Problems
D. A Way of Overcoming Insomnia
E. Sleep Problems of Long and Short Sleepers
F. Oversleeping — Too Much of a Good Thing
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Although the dangers of too little sleep are widely known, new research suggests that people who sleep too much may also suffer the consequences.
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Investigators at the University of California in San Diego found that people who clock up 9 or 10 hours each weeknight appear to have more trouble falling and staying asleep, as well as a number of other sleep problems, than people who sleep 8 hours a night. People who slept only 7 hours each night also said they had more trouble falling asleep and feeling refreshed after a night’s sleep than 8-hour sleepers.
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Previous studies have shown the potential dangers of chronic(慢性的) shortages of sleep — for instance, one report demonstrated that people who habitually sleep less than 7 hours each night have a higher risk of dying within a fixed period than people who sleep more.
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For the current report, Kripke reviewed the responses of 1,004 adults to sleep questionnaires, in which participants indicated how mush they slept during the week and whether they experienced any sleep problems. Sleep problems included waking in the middle of the night, arising early in the morning and being unable to fall back to sleep, and having tiredness interfere with day-to-day functioning.
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Kripke found that people who slept between 9 and 10 hours each night were more likely to report experiencing each sleep problem than people who slept 8 hours. In an interview, Kripke noted that long sleepers may struggle to get rest at night simply because they spend too much time in bed. As evidence, he added that one way to help insomnia is to spend less time in bed. “It stands to reason that if a person spends too long a time in bed, then they’ll spend a higher percentage of time awake,” he said.