一、表语从句常用引导词：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；雅思真题里相关例句很少；

who 在从句里充当成分，指人，不指物；雅思真题里相关例句很少；

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 用法比较复杂，有多种限制，而且雅思真题里相关例句很少；

二、剑桥真题例句：

1. Another factor thatmay boost the prospects for AI in the near future is that investors are now looking for firms using clevertechnology, rather than just a clever business model, to differentiatethemselves.(C5P72L22)

2. The criticalquestion now is  whether  this can becomethe norm, rather than the exception. (C5P87L41)

3. This is  what  would have made the whole thing work.(C10P73L25)

4. This was  how ,in 1660, the renowned French grammarians of the Port-Royal abbey nearVersailles distilled the essence of language, and no one since has celebratedmore eloquently the magnitude of its achievement. (C11P97L12)