1. I started learning English three years ago.

→ I have learned English for three years. 

2. I have never met him for three years.

→ I last saw him three years ago.

3. We have studied French for 4 years.

→ We started To study French 4 years ago.

4. I haven't seen her for a long time.

→ I didn't see her for a long time.

They have worked in that factory since 1996.

-> They started to work in that factory in 1996.

6. How long have you learnt English?

→ How long ago did you learn English? 

7. He has seen her when he was 12.

→ He started to see her when he was 12.

8. Lan hasn't written to me for a month.

→ Lan didn't write to me a month ago.

9. My father started to give up smoking last year.

→ My father has given up smoking for a year.

10. When did you start to listen to classical music?

→ How long have you listened to classical music?

11. I last saw her 10 years ago.

→ I haven't seen her for 10 years.

12. How long have you bought this car?

→ When did you buy this car?

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