Question

大神帮解一下英语题目，急求，谢谢

In a word,good books can let me know () I didn't know before.
请问为什么不能填that呀，正确答案是what，谢谢。

Answer 1

这是个宾语从句。
that是连词，在从句中不能作成分。这里know后面少了宾语，所以不能用that
In a word, good books can let me know what I didn't know before.
总之，好书可以让我知道我以前所不知道的。