B考查as引導的定語從句
as可以代替整個句子或一件事,引導非限制性定語從句,在從句中作主語、賓語或表語,意為“正如……,就像……,據……”；從句位置可置于主句之前或之后,有時也可作為插入語置于句中,一般用逗號和主句隔開.
as的這種用法常見于以下這些結構:as we can see, as
can be seen, as we know, as is（well） known, as may be imagined, as often happens, as has
been said before, as was mentioned above, as is often the case, as/indeed it
is…
例:As is well known,great changes have taken place in China. 或Great changes, as is well known, have taken place in
China.眾所周知,中國發(fā)生了巨大的變化.( as在定語從句中作主語.)