6. They have learnt English for four years now.
--> They started to learn English four years ago
7.I last saw her three years ago
--> I haven't seen her for three years
8.I have’t seen my brother for four years.
--> I last saw my brother four years ago.
9.She started to give up smoking last year.
--> She has given up smoking since last year
10. Tom and Marry have worked in that factory since 1990
-->Tom and Marry started to work in that factary in1990
* Giải thích:
- S + started + to V + O + .... (thời gian) + ago = S + has/ have + V-PII + O + since/ for + thời gian
- S + last + V - ed + O + .... (thời gian) + ago = S + has/ have not + V - PII +O + since/ for + thời gian