`15.`  The last time he wrote to me was in April.

`16.` She last had a swim five years ago.

`17.` They haven't talked to each other for two months.

`18.` She hasn't seen her elder sister since 1999.

`19.`  It's years since she wrote to me.

`20.` It's ten years since Robert and Catherine got married.

_____________________________________

`o.` Thì hiện tại hoàn thành`:` S + have/ has + V(pp) + since + mốc thời gian.

`->` Thì quá khứ đơn `:` The last time + S + Ved/ V2 + to be + in + thời gian.

`o.` Thì hiện tại hoàn thành`:` S + have/ has + not + V(pp) + for + khoảng thời gian.

`->` Thì quá khứ đơn`:` S + last + Ved/ V2 + khoảng thời gian + ago.

`o.` S + have/ has + (not) + V(pp) + for + khoảng thời gian.

`->`  It's + khoảng thời gian + since + QKĐ.

 15.The last time he wrote to me was in April.

(The last time + S + Vqk + … + was+ mốc thời gian

=S +hasn’t / haven’t + V3/ed + … since + mốc thời gian.)

 16. She last had a swim five years ago.

(The last time + S + Vqk + … + was + khoảng time + ago.

=S +hasn’t / haven’t + V3/ed + … for + khoảng thời gian.))

17. They haven't talked to each other for two months.

(S+last+Vqk+khoảng thời gian+ago

=S+haven't/hasn't+VpII+for+khoảng thời gian.)

18. She hasn't seen her elder sister since 1999.

(The last time + S + Vqk + … + was + khoảng time + ago.

=S +hasn’t / haven’t + V3/ed + … for + khoảng thời gian.))

19. It's years since she wrote to me.

(It's + khoảng thời gian ….+ since+ S+Vqk

=S+haven't/hasn't+VpII+for+khoảng thời gian.)