1. They are opening their books. (They open their books. Если имеется в виду постоянное, обычное действие-но это вряд ли)
2. Put these exercise books on that table.
3. Take my exercise book and give me yours.
4. She only thinks about herself.
5. He must answer the question himself.
6. This book is mine, not yours.
7. Have you seen this film? Yes, I saw it yesterday.
8. He gave us his books and asked to give them back the next week.
9. Don't worry, we can take the letters to the post office ourselves.
10. Here is his pen. And where is mine?