as 引导定于从句:1、as用作关系代词和关系副词引导限定性定语从句,并在从句中做主语、表语和状语,构成the same .as, such.as等结构。Eg: I have got into the same trouble as you.2、 as引出非限定性定语从句时,代替整个主句,对其进行说明。但通常用于:(as we all know, as it is known, as is known to all, as it is, as is said above, as always mentioned above, as is usual, as is often the case, as is reported in the newspaper) .as在非限定性定语从句中作主语、表语或宾语,且引出的从句位置比较灵活,可位于句首或句末,也可置于主句中间。通常均由逗号将其与主句隔开。as有“正如, 就像”之意。Eg:As is known to the United States, Mark Twain is a great A