If city noises ____ from increasing, people ____ shout to be heard even at the dinner table 20 years from now.
A. are not kept; will have to B. are not kept; have to C. do not keep; will have to D. do not keep; have to(全国高考,92-31)
答案为 A。但是, are kept from 是什么意思呢?
are kept from 是 keep...from 的被动形式。keep...from 的意思是：“防止”“避免”“阻止”：
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The government is considering further action to keep the pound from falling in value. 政府正考虑采取进一步措施以防英镑贬值。
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You can't keep me from going out! 你不能不让我出去!
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China, with the region's fastest-growing economy, had kept the crisis from growing even worse by refusing to devalue its currency. (B. Clinton, My Life) 中国拥有该地区增长最快的经济，而且承诺人民币不贬值，这阻止了危机的进一步恶化。（《我的生活》）
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It keeps him from worrying so much about being a dog. (B. Clinton, My Life) 这样它就不会老为自己是条狗而烦恼。(《我的生活》)
[试题句意]如果不能防止城市噪音的增大,那么从现在起20年后,甚至在饭桌上人们也不得不大喊大叫,彼此才听得见。