1. I can’t/am not able to answer this question.
2. When I was three I could/was able to understand what I was told.
3. I can/am able to call you tomorrow.
4. Could you/Are you able to answer the phone, please?
5. My sister can’t/isn’t able to sing but she can/is able to dance.
6. I can/will be able to perform this trick in two weeks.
7. The fireman could/was able to save the cat.
8. I can’t/couldn’t visit you this week.
9. Can/Could you speak German?
10. The doctor is free. He can/is able to examine you.