短文填空。（共10分，每小题1分）
阅读短文，并选择方框中的词用适当形式填空，每个词最多选用一次，有一项是多余的，每空一词。
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Sometimes, we see some people reading books while biting their nails (咬指甲). According to the BBC(英国广播公司), up to 45 percent of teenagers bit their nails. There is not an exact answer to     why people bite their nails. But most commonly, nail biting is said to be a nervous habit. It is done     of stress(压力), boredom or excitement.
What’s more, a report says that people with higher levels of intelligence(智力)     biting their nails at an early age. It believes that compared    common person,     with higher levels of intelligence may feel higher levels of stress more easily.
This habit is    for the biters. It can give them red or sore fingertips. And long-term nail biting can affect(影响)    nails grow.
But don’t worry! There are many    to stop biting your nails. First, keep your nails clean. The more you focus on taking care of your nails, the   likely you may bite them again. Also, when you feel stressed, try to relax.    exercise or having a warm bath both help.