as they are是一个非限制性定语从句，意思是“正如他们一样”。

r 关系代词as引导定语从句时，等于which fact，前面有逗号，因此它引导的是一句非限制性定语从句，可出现在句首、句中或句尾，并且没有明显的先行词，这句非限制性定语从句修饰的是前面的一整句句子。as在定语从句里可以作主语、宾语和表语。如：

r The earth is round, as is known to all.

r The elephant is like a snake, as everybody can see.

r Oil and water don't mix, as we all know.