三、主语从句常用引导词：that, what, which, who, how, whether, if。

that 在名词性从句中只负责把从句引出来，不在从句里充当成分，这点和在定语从句里的用法不同，定语从句中that充当成分；

what 一般不用于定语从句，用在名词性从句里既引导从句，又在从句里充当成分；

which 在名词性从句里含有“哪一个”的意思，通常有一定的选择范围，而在定语从句里则没有意思，只是引导句子和充当句子成分；

who 在从句里充当成分，指人，不指物；

how 表示“如何”，可以用来表示程度；

whether 表示“是否”，不管是主语从句，表语从句，宾语从句里都可以使用；

if 在名词性从句里也表示“是否”，而不是条件状语从句里“如果”的意思；

四、剑桥真题例句：

1. It’s a mass extinction, and whether we will ever rebound from the loss is difficult toknow.(C4P42L24)

2.It is also accepted thatthis right generates an obligation or duty for the state to ensure thatadequate health-care resources are provided out of the public purse. (C4P98L8)

3.What Milgramwas trying to discover was the number of teacher-subjects who would be willingto administer the highest levels of shock, even in the face of strong personaland moral revulsion against the rules and conditions of theexperiment.(C5P20L27)

4. When the Lumiere Brothers and other pioneers began showingoff this new invention, it was by no means obvious how it would be used. (C6P64L11)

5. The main reason why geo-engineeringis supported by many in the scientific community is that most researchers havelittle faith in the ability of politicians to agree --- and then bring in ---the necessary carbon cuts. (C11P26L23)