As 引導非限定性定語從句時與which的區別：當主句和從句語義一致時，用as;反之，用which。

　　如：He made a long speech, as was expected.

　　He made a long speech, which was unexpected.

　　Tom drinks a lot every day, which his wife doesn’t like at all.

　　(3)但是，如果從句和主句的動作在將來不同的時間發生，則兩部分都要用來將來時，

　　注：⑤在“介詞+關系代詞”的結構中，也可用復雜介詞，如：by means of (用，依靠)，as a result of (作為結果)等：

　　例：I have three children, one daughter and two sons, all of whom graduated from the same university .

　　我有三個孩子：一個女兒、兩個兒子，他們都畢業于同一所大學。

　　The police, in whom I have great confidence, are trying to find out who did it.

　　我對警察有極大的信心，他們正在努力尋找是誰做的這件事。

　　This is the part of the river in which I like to swim.

　　(in which=where)

　　我喜歡在這條河里面游泳，這就是(我喜歡游的)那個地方。

　　The man from whom you bought the house is my uncle.

　　你從他那里買下房子的那個人是我叔叔。

　　This is the desk by means of which he jumped over the wall.

　　這就是他用來跳過墻去的那張桌子。

　　She was running a fever, as a result of which she failed in the exam.

　　她當時正發燒，所以考試失敗了。

　　He is the man from whose house the picture was stolen.

　　他就是那個家里的畫被偷了的人。

　　注：⑥一個先行詞后面可以跟一個以上的定語從句，這種現象叫雙重關系從句：

　　例：Here are some words which are often used but which are very confusing.

　　這里有些常用但非常混亂的詞。

　　He is the only person that I can find who is able to solve the problem.

　　他是我能找到的唯一解決這個問題的人。

　　名詞性從句

　　在主從復合句中，從句可以充當主句的主語、表語、賓語或同位語。由于在多數情況下，主語、表語、賓語或同位語這四種句子成分由名詞性詞類充當，所以，我們把這些作用相當于名詞的從句統稱為名詞性從句，把充當主語、表語、賓語或同位語的從句分別稱為主語從句、表語從句、賓語從句或同位語從句。也就是說充當什么成分就叫什么從句。名詞性從句由連接詞(或關聯詞)引導。

　　常用的連接詞有：

　　疑問詞(who, whom, whose, what, which, where, why, when, how)可以引導主語、賓語和表語從句。

　　它們的特點是：1、疑問詞有本身的詞義;2、疑問詞在從句中擔當句子成分，如主語、賓語或狀語;3、這種疑問詞引導的從句一律用陳述語序，不能用疑問語序。