1. You can't teach an old dog new tricks. 

2. You cannot teach an old dog new tricks.

3. Teach an old dog new tricks.

4. Stop trying to teach an old dog new tricks; you are just wasting time.

5. Yet(), some people say that you can never teach an old dog new tricks.

6. Mavis: I'm not so sure. You can't teach an old dog new tricks you know.

7. My secretary has been using that old manual typewriter for more than twenty years and I cannot get to change to a word processor; it seems you can't teach an old dog new tricks.

8. Yet, some people people say that you can never teach an old dog new tricks.

9. Mom : Honey, don't even try . You can't teach an old dog new tricks.

10. She yelled at me and told me that she couldn't teach an old dog new tricks.