=>
11. Samuel has kept a diary since 1997.
-> chuyển QKĐ sang HTHT, S have/has (not) V3/ed, since + mốc thời gian
12. We have learned English for five years.
-> chuyển QKĐ sang HTHT, S have/has (not) V3/ed, for + khoảng thời gian
13. I have lived in Ho Chi Minh City since I was 8.
-> chuyển QKĐ sang HTHT, S have/has (not) V3/ed, since + mốc thời gian
14. She started teaching the children in  this remote village five months ago.
-> started Ving : bắt đầu làm gì
15. The last time he wrote to me was in April.
-> the last time S V2/ed (lần cuối)
16. She last had a swim five years ago.
-> S last V2/ed
17. They haven't talked to each other for two months.
-> chuyển QKĐ sang HTHT, S have/has (not) V3/ed, for + khoảng thời gian