(1) as 和which都可引導非限制性定語從句，放在主句之後；在非限制性定語從句中充當從句的主語、賓語或表語。如：
Tom has found a good job, as / which we all hope. 湯姆找到了一件好工作，這正是我們大家所希望的。
(2) as 和which都可代表整個句子的內容或主句中的某一成分。如：
His mother is ill, which makes him very sad. 他母親病了，這件事情使他很難過。
當先行詞前面有so + adj. + a / such + (a) + adj. , the same等詞修飾時，引導詞只能用as，而不用which。如：
She is so nice a girl as we all like. 她是個我們大家都喜歡的如此好的女孩。
as 在從句中常作賓語；作主語時，從句的謂語動詞常為系動詞，即：系表結構或被動結構。如：
As you expected, he turned up on time. 正如你所願，他按時到了。
As is said above, he has conquered the difficulty. 正如上面所說，他征服了困難。
當非限制性定語從句放到主句的前面時，引導詞只能用as，而不用which。如：
As is planned, we got there before eight. 正如計劃，我們再把店前到達了那兒。
As引導的非限制性定語從句指表示積極的意義，與主句是順理成章的關係，絕不能與之矛盾。若非限制性定語從句表示一種消極的意義，則只用which。如：
He has succeeded in his career, as / which we all hope. 他在事業中成功了，這正是我們大家所希望的。
當非限制性定語從句的引導詞前面有介詞時，只能用which, 而不可用 as。如：
He has a new computer, for which he paid nearly ten thousand yuan. 他有一臺新電腦，這臺電腦花了他將近一萬元。
(1) as 和which都可引導非限制性定語從句，放在主句之後；在非限制性定語從句中充當從句的主語、賓語或表語。如：
Tom has found a good job, as / which we all hope. 湯姆找到了一件好工作，這正是我們大家所希望的。
(2) as 和which都可代表整個句子的內容或主句中的某一成分。如：
His mother is ill, which makes him very sad. 他母親病了，這件事情使他很難過。
當先行詞前面有so + adj. + a / such + (a) + adj. , the same等詞修飾時，引導詞只能用as，而不用which。如：
She is so nice a girl as we all like. 她是個我們大家都喜歡的如此好的女孩。
as 在從句中常作賓語；作主語時，從句的謂語動詞常為系動詞，即：系表結構或被動結構。如：
As you expected, he turned up on time. 正如你所願，他按時到了。
As is said above, he has conquered the difficulty. 正如上面所說，他征服了困難。
當非限制性定語從句放到主句的前面時，引導詞只能用as，而不用which。如：
As is planned, we got there before eight. 正如計劃，我們再把店前到達了那兒。
As引導的非限制性定語從句指表示積極的意義，與主句是順理成章的關係，絕不能與之矛盾。若非限制性定語從句表示一種消極的意義，則只用which。如：
He has succeeded in his career, as / which we all hope. 他在事業中成功了，這正是我們大家所希望的。
當非限制性定語從句的引導詞前面有介詞時，只能用which, 而不可用 as。如：
He has a new computer, for which he paid nearly ten thousand yuan. 他有一臺新電腦，這臺電腦花了他將近一萬元。