Найти ошибку. Помогите)

71. I don`t know the boy. I`ve never met him.
2. How long does it take you to clean your room?
3. It is raining hard. Let`s stay at home.
4. There will be a museum in this square next year.
5. Have you invited many people to the New Year party?
6. Who washed the floor
7. I am sure the film will be interesting.
8. Has he locked the door? - Yes, he has.
9. Will there be any books for the boys?
10. They bought this book three months ago.