as 在定语从句中是关系代词，可做句子成分。但在上述两个句子中，as只是在引导定语从句而已，不作句子成分。as 引导非限制性定语从句，可放在主句之前，或者主句之后，甚至可以切割一个主句；which引导的非限制性定语从句只能放在主句之后。另外，as有“正如……，正像……”的意思(1) As is known to all, China is a developing country.(2) He is from the south, as we can see from his accent.(3) John, as you know, is a famous writer.(4) He has been to P
