I am having a hard time understanding active voice. Can anyone please assist?

which following sentence is active voice?
1. The new product line was developed by the Research and Development department?
2. The secretary was promoted by her supervisor to an assistant position.
3. The land developer signed the contract yesterday.
4. It was determined that sales have fallen significantly.
Thanks

1. Who actually did the developing?

2. Who did the promoting?

3. Who signed the contract?

4. Who did the determining?

When a verb is in active voice, that means the subject is doing that action. In #3, your answer should be "developer" and that's right -- the subject "developer" did the action of the verb "signed."

What would you say about the other 3?