下面我们结合例句来看一下由that, which, who和whom引导的定语从句：
如：A plane is a machinethatcan fly. (作主语，指物)
That’s is the best hotelthatI know. (作宾语，指物)
Who is the manthatis reading a book over there? (作主语，指人)
The girlthatwe saw yesterday is Jim’s sister. (作宾语，指人)
如：They planted some treeswhichdidn’t need much water. (作主语，指物)
The fishwhichwe bought this morning were not fresh. (作宾语，指物)
如：The boywhobroke the window is called Tom. (作主语，指人)
The person towhomyou talked just now is Mr Smith. (作宾语，指人)
引导宾语从句的词有：连词that, whether, if；连接代词who, whose, what, which；连接副词when, where, how, why等。
如：I doubtwhetherhe will succeed.
I wonderwhathe’s writing to me about.
I’ll tell youwhyI asked you to come.
如：I don’t knowwho all the people are.
Please find outwhen the ship sails for New York.
He was afraidthat the other kids would laugh at him.
如：I finditstrangewhat she said at the meeting.
We have madeitclearthat we will learn to deal with various difficult problems.