单项选择： 

1. I have bought two pens,____write well. 

A.none of which   B.neither of which  C. both of which   D.all of which 

答案：C。根据前面的 two，可知这里是“两者”，故可排除 A 和 D（它们用于三者），再根据空格后用的是 write 不是 writes，可知要选 both of which。如果不理解这类用法，可通过添加连词 and 来帮助理解：

I have bought two pens, both of which write well. 

=I have bought two pens, and both of them write well. 

2.There is a great deal of oxygen around us,____we couldn’t live. 

A.without it   B.which   C.without which   D.that

答案：C，

There is a great deal of oxygen around us, without which we couldn’t live. 

=There is a great deal of oxygen around us, and without it we couldn’t live.