解析　句意为：是否能找到制止污染的方法是公众所担心的。所选项引导表语从句，并在从句中作主语，故用what；which哪一个；that引导名词性从句时，在从句中不作任何成分；where作状语。

6．Some children want to challenge themselves by learning a language different from ________ their parents speak at home.

A．what B．that C．which D．one

答案　A

7．________is known to us all is that the 2012 Olympic Games took place in London.

A．It B．What C．As D．Which

答案　B

解析　本题考查名词性从句的连接词辨析。空格处内容作第一个is的主语，同时它引导的从句又作第二个is的主语，故用what引导主语从句。

8．________matters most in learning English is enough practice.

A．What B．Why C．Where D．Which

答案　A

解析　本题考查主语从句的连接词辨析。what引导的从句作句子的主语，同时又在从句中作主语。

9．It is none of your business________other people think about you.Believe in yourself.

A．how B．what C．which D．when

答案　B

解析　本题考查连接词用法辨析。空格处内容要作think的宾语，所以排除A、D两项；从上下文看出，本题没有选择范围，所以排除C项。

10．The problem is not ________ we leave，but ________ we can get there.

A．when；how B．when；where

C．how；which D．where；when

答案　A

解析　句意为：问题不是我们什么时候离开，而是怎么到那儿。

11．The last time we had great fun was________we were visiting the Water Park.

A．where B．how C．when D．why

答案　C

解析　本题考查名词性从句的连接词辨析。根据句子结构可知空格后所接的是一个表语从句，从句所表示的是一个时间点，故选when。