Rewrite the following sentences using the past perfect tense. Ensure the past perfect is used correctly with "before", "after", "because", or "by the time".

Here are the rewritten sentences:

7. I had fastened my seat belt before the plane took off.
8. The company collapsed after it had made several poor decisions.
9. They had broken the window before the children ran away.
10. She spoke before everyone had formed their own opinion.
11. After she had packed her bags, she locked the door.
12. The bell had rung before the students left the classroom.
13. He was nervous because he had forgotten his speech notes.
14. By the time the teacher arrived, the class had started the test.
15. After she had finished the project, she sent it to her manager.
16. We didn't recognize the place because the city had changed a lot.
17. She had washed her hands before she had lunch.
18. He apologized after he had made a serious mistake.