在句20中where是引导定语从句，而在句21 中where是引导在点状语从句的。

b. 定语从句还是主语从句

22. As is known to all, they are sure to win.

23. It’s known to all that they are sure to win.

在句22中as是关系代词，代表后面的整个句子做主句的主语。在句23中it是代词，代表that引导的句子做主句的主语。

九.看不出插入句部分，以为是定语从句，影晌句中动词的选择

24. I met a man who I thought _____ to help us.

a. would come b. of coming c. to come d. come

许多学生一看though马上就想起think of doing sth而选了c. 然而在这里I thought是一个插入成份，如果将其省掉就容易看出who是后面的主语了。同样who也不会用whom 了。

分辨不出限制性定语从句，非限制性定语从句有一些分别：

25. All the books here, which have beautiful pictures in them, were written by him.

26. All the books here which have beautiful pictures in them were written by him.

句25 一般表示所有的书都是他写的。句26则表示所有有图画的书是他写的。

27. My father, who works in Shanghai, writes to me twice a month.

28. My father who works in Shanghai writes to me twice a month.。

同样27，28一般的情况下是略有不同意义的。想想下句,如无逗号意义怎样。

29。He sent a letter to his wife, who works in the south of China.

十.冠词处理不好