2012考研必备：考研英语语法精要(39)

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4.as 与which用作关系代词的区别
     (1)as与the same, such, so, as等关联使用。如：
    As the forest goes, so goes its animal life.
    (2)as和which都可以引导非限定性定语从句，但as在句中的位置比较灵活，可出现在句首、句中、句末，而which只能出现在句末，尤其是当先行词是整个句子时。如：
    As is true in all institutions, juries are capable of making mistakes.
    As is generally accepted, economic growth is determined by the smooth development of production.
    常见的这类结构有：
    as has been said before, as has been mentioned above, as can be imagined, as is known to all, as has been announced, as can be seen from these figures, as might/could be expected, as is often the case, as has been pointed out,
    as often happens, as will be shown等。