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名词(包括代词)。单复数问题。一般判断方法：对比主语跟宾语。主语跟宾语的单复数形式必须相同。也可能会根据谓语或者定语进行判断。下面是例题。
No matter when they came from or what their previous lifestyle is, the refugees were grateful for having been granted political asylum in the United States. No error.
请看what their previous lifestyle is这段话中 their跟lifestyle的单复数不同，当然还有后面的is也一起错了。应该改成lifestyles are.
动词。主谓一致的单复数问题。时态错误。过去式的单词错误。时态错误主要发生在主句和从句的时态不一致。词汇错误就是有些不规则动词的过去式用错，比如常见的hang、rise等等，当然也有drove写成drived的。一般判断方法：看到动词，要本能的反应是单复数、时态问题，如果都没有就考虑词汇用错问题。
Air pollution caused by the industrial fumes has been studied for years, but only recently has the harmful effects of noise pollution become known. No error.
这里面only recently has the harmful effects of noise pollution become known使用了倒装。The harmful effects是主语，has是谓语，所以现在答案很明显了吧。
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