*Giải thích:

- The last time + S + Ved/V2 + O + was + time (trong QK)

-> S + has/have + not + Vpp + O + for/since + time (trong QK)

- It's + time (trong QK) + since + S + (last) + Ved/V2 + O 

-> S + has/have + not + Vpp + for/since + time (trong QK)

- S + started/began + to V/V-ing + O + time (trong QK)

-> S + has/have + Vpp + for/since + time (trong QK)

- This is the first time + S + has/have + Vpp + O 

-> S + has/have + not + Vpp + ... + before

-> S + has/have + never + Vpp + ... + before

* Answer : 

`51` I haven't gone swimming since we were in Spain

`52` It's weeks since you (last) tidied this room 

`53` We have looked for a flat for 2 months and we are still looking

`54` I haven't been to a night club before

`55` This is the first time they have heard such a thing

`56` This is the first time his authority has not been challenged (Câu bị động thì Hiện Tại Hoàn Thành : S + has/have + been + Vpp + by O)

`57` It is 2 years since she (last) left university

`58` I have never known a more warm-hearted person than my mother

`59` It is over a year since I last saw them 

`60` It has rained since 2 o'clock