找出下列句子中的错误，并总结出规律：
1. Can you tell me how many students are there in your class?
2. I don't know where has he gone.
3. The owner of the shop came to see what the matter was.
4. We suggested that we would go to the cinema.
5. My idea is that we must do our homework first.
6. His proposal that we went there on foot is acceptable.
7. If we will have a meeting hasn't been decided yet.
