如果是名詞性從句(主語、表語、賓語等從句)，缺少賓語，可以用what.

從句缺主語時，引導詞都可以用which 和that

1.

當先行詞是everything, anything, nothing (something 除外), all, none, few, little, some等代詞時，或當先行詞受every, any, all, some, no, little, few, much等代詞修飾時。如：

2.

　　Have you taken down everything that Mr. Li said?

李老師講的你都記下來了嗎?

　　There seems to be nothing that is impossible to him in the world.

對他來說似乎世界上沒有什麼不可能的事。

　　All that can be done has been done. 所有能做的都做好了。

　　There is little that I can do for you. 我不能為你幹什麼。

　　He stayed in the library and looked up any information that they needed.

他呆在圖書館查詢所需的資料。

　　注意：當先行詞指人時，偶爾也可用關係代詞who，如：

　　Any man that / who has a sense of duty won’t do such a thing.

任何有責任感的人都不會做這樣的事。

　　All the guests that / who were invited to her wedding were important people.

所有應邀來參加她婚禮的客人都是重要人物。

2.當先行詞被序數詞修飾時。如：

　　The first place that they visited in London was the Big Ben.

在倫敦他們參觀的第一個地方是大本鐘。

3.當先行詞被形容詞最高階修飾時。如：

　　This is the best film that I have ever seen. 這是我看過的最好的電影。

4.當先行詞被the very, the only修飾時。如：

　　This is the very dictionary that I want to buy. 這正是我要買的詞典

可以用what，which和who。這些特殊疑問句詞具有名詞或代詞的語法功能，在句子中作主語，賓語和同位語。what，which 表示“事物”，who表示“人”。例如：

1.This is what was done by your son while you were away.

2.The difficulty I have to deal with is which of the two jobs should be chosen.

3.The question I should answer is who did the best.

表語從句缺主語引導詞用what，具體內容如下。

表語從句（Predicative Clause）就是用一個句子作為表語。

表語（Predicative）的作用：說明主語是什麼。可以由名詞、形容詞或相當於名詞或形容詞的詞或短語充當表語的成分。

然而要注意，表語從句屬於名詞性從句，只是表語的其中一種情況——由名詞充當表語。