英语从句问题？？！

从句中能出现助动词do吗？能出现can，may等情态动词吗？还能出现be动词吗？请各位英语高手举例说明，并说说从句的结构和不能出现什么，能出现什么的一些注意事项！谢谢！

主从关系 应该是逐句+连词+从句

从句应该是陈述语序，而且从句中必须有谓语动词 （从句智慧却助于，宾语或者状语之类的）

然后根据先行词和从句中所缺的成分选择关系代词，如果从句结构完整（即主谓宾齐全）则使用关系副词

当先行词是物，且从句缺宾语时，注意判断从句的谓语动词是及物的还是不及物的``若是及物动词则连词不能用which只能用that

见到that 就应联想到从句

主+谓+that+主+谓

1. 从句的根本是“从属连词+ 陈述语序”。

Do you know where they are from?

不可以说：Do you know where are they from?

2. 从句中肯定有主谓关系，即 必有谓语动词形式。所以就会出现助动词、情态动词、BE动词。

If I am not invited, I won't go to the party on Saturday evening.

That's because they can't meet the deadline.

The reason is that he don't like Jazz music.

Do you know of the girl who is in red?

His suggestion was that she (should) come earlier tomorrow.