2012考研必备：考研英语语法精要(52)

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3.比较从句中主语的省略
    在这种省略结构中，也可以把than或as当成关系代词。因为主语省略了，所以尤其要注意识别哪个词是省略了的主语，进而选择谓语的数、时态和语态。
    These proposals sought to place greater restrictions on the use and copying of digital information than exist in traditional media.
    There ought to be less anxiety over the perceived risk of getting cancer than exists in the public mind today.
    The project requires more labor than has been put in because it is extremely difficult.
   
    4.that用于引导宾语从句时，可以省略