Check my answers please

Dear teachers,

The correct answers are marked in blue below. But could you please explain me, why those are the correct answers?

1.Pray and give _________ to God that you have been saved.

1. thanking
2. thank
3. thanks
4. thanked
For the above one, I feel 'thanks' is the correct answer, but it is not.



2.We were given a brief _________ of the chapter.

1. introduce
2. introduction
3. introducement
4. introducing
For the above one, I feel 'introduction' is the correct answer, but it is not.


3.Why can’t you go home ______?

1. by you
2. by ownself
3. by oneself
4. yourself
For the above one, I feel 'by yourself' is the answer, but it is not.

Thanks.