1. knows, doesn't know
2. It is raining.
3. drinks, is drinking
4. have lost
5. have been writing, have already finished
6. Have you ever been to China? No, I haven't, but I've been to Japan twice.
7. have been typing, have already typed
8. has been making, How many cakes has she made?
9. Fred often writes the letters to his friend, doesn't he?
10. has been translating
11. Where do you usually spend your weekend?
12. Who is playing computer games now? Sam and Bob are.
13. What language does Mr Brown teach at the institute?
14. have walked, have been walking
15. has broken