IT 还是WHAT?急等.______sometimes keeps her awake at night is that Tom is getting more and more quiet at home.为什么不填What

IT 还是WHAT?急等.
______sometimes keeps her awake at night is that Tom is getting more and more quiet at home.
为什么不填What

答案不应用It而应用What,原因如下：前面是主语从句,且主语从句缺少主语,故采用连接代词What引导主语从句.代词it只能作主语但不能引导从句.句中is之后that引导表语从句.

绝对是答案错了。。肯定是what

显然答案错误

你听谁说的，这里是WHAT。
主语从句啊

不是吧。。填WHAT吧？？
不然句子结构怎么解释？？

答案错了 是what啊 主语从句