另外，如果which或whom在定语从句中原为介词的宾语，则这个介词可以提到从句前，构成介词+which或whom引出的定语从句。
定语从句根据与先行词的密切程度可分为限制性定语从句和非限制性定语从句。限制性定语从句与先行词关系密切，从句是整个句子不可缺少的部分，去掉之后句子的意思就不完整，不明确，从句与主句之间不用逗号隔开。非限制性定语从句与先行词的关系比较松散，从句只是对先行词的附加说明，去掉之后句子的意思仍然很清楚，从句与主句之间常用逗号隔开。
将下面每组中的两个句子合并，将其中一个改为定语从句。
1) I went to visit the American author.
He wrote a number of books about China.
2) My aunt prepared the soup.
I ate the soup.
3) I have an arrangement with my bank.
By the arrangement they let me use their money and repay them next month.
4) He sent her a letter.
In the letter he said that he was sorry for what he had done to her.
5) Mr. Brown just came from Britain yesterday.
He will teach us accounting this term.
6) She is going to spend the winter holidays in Hainan.
She has some relatives there.
7) The United States is known for its supermarkets.
In these supermarkets, huge quantities of all kinds of food and household articles are sold.
8) The story happened in late 19th century.
At that time, China is suffering from the invasion of western powers.
状语从句
状语从句按其意义可以分为时间、地点、原因、目的、结果、条件、方式、让步等类别。其引导词分别如下：
时间状语从句：when, after, before, as, while, whenever, since, once, until, as soon as
地点状语从句：where, wherever
原因状语从句：because, as, since, now that
目的状语从句：so that, in order that, lest
结果状语从句：so that, so…that, such…that
条件状语从句：if, unless, suppose (supposing), provided (that), providing (that), on condition (that), in case, as (so) long as
方式状语从句：as, as if (though)
让步状语从句：though, although, even if (though), however, whatever, no matter how (what, where, when), whether…or