not....but...的用法

1、What makes his parents worry is not his grades but that he hasn't any interest in learning.

2、Your answer is not wonderful but acceptable。

A、这两句话是不是一样的结构，但是第一句but后面跟的是从句，所以要加that呢？that后是不是一个名词性从句呢？B、 第一句如果but后面是名词，是不是就不用that了？如：What makes his parents worry is not his grades but his health.

【答】not A but B：是一个很明显的“舍取关系”。A 和 B 虽然是并列，但不一定要平行，成分可以不对等。

第1句中的 his grades 是名词词组，而 that he hasn't any interest in learning 是一个表示陈述意义的名词性从句。这两个成分都可以取代或者回答前文的 What，后两句是取代what 的结果，对照如下：

What makes his parents worry

His grades makes his parents worry.

That he hasn't any interest in learning makes his parents worry.

所以，使用that 从句作句子主语没有任何问题，这就是我们常说的主语从句。注意：that 引导名词性从句作主语时，不可省略。