inversions and frontings of objec

Hello, everybody.

I have some questions about inversions and frontings of objects. For non-natives speakers, they are really confusing things, which are different from what I have learned from common English books. Would you take a look at the below sentences?

1. The students forgot some things.
2. Some things the students forgot.
3. Some things did the students forgot.
4. Some things forgot the students.
5. Some things did forget the students.
6. Some things forgot the students who didn't usually forget anything.
7. Some things the students forgot who didn't usually forget anything.

I really appreciate it if you teach me which sentences sound unnatural.
Many thanks in advance.

Many thanks in advance.