which和as都可以引导非限制性定语从句,用来代表所修饰的整个主句,但用法不同。as所引导的定语从句可以理解为带有宾语从句的主从复合句,而which所引导的非限制性定语从句则不能这样理解。例如: 1.As all his friends agree, he was unusually warm-hearted, loving and generous. 此句中as指He was unusually warm-hearted, loving and generous. 在从句中做动词agree Both which and as guide non-restrictive attributive clauses to represent the entire main sentence modified, but with different usages. The attributive clause led by as can be understood as a master-slave compound sentence with an object clause, and the non-restrictive attributive clause guided by which cannot be understood in this way. For example: 1.As all his friends agree, he was unusually warm-hearted, loving and generous. In this sentence as means He was unusually warm-hearted, loving and generous.