给下列句子中的宾语从句加下划线,并将它们的引导词刷色（无实际意义、可以省略的加粗；有具体意义、不可省略的加下划线）

1, I said that I would be at your house at six o'clock,
that后面都是宾语从句,that无实际意义
2. I don't know when I'll finish.
when后为宾从,有意义
3. My wife wants to know if Mary needs any help.
if后为宾从,有意义
4. I don’t know why they didn’t come.
why后为宾从,有意义
5. Tell me what you are talking about.
what后为宾从,有意义
6. They thought that they could win a lot of money.
that后为宾从,无意义