`21.` She has worked as a secretary for five years.

Giải thích: $\text{S + started + V-ing/to V = S + have/has + Ved/V3}$

`22.` When did they buy the house?

Giải thích: $\text{(-Wh) Did + S + V-bare + ...?}$

`23.` It's the first time I have ever met such a famous person.

Giải thích: $\text{It's the first time + S + have/has + ever + V3/V-ed + such + O}$

`24.` I have been working for the company for a year

Giải thích: $\text{S + have/has + been + V-ing}$

`25.` I haven't seen him since I was a student.

Giải thích: $\text{S + have/has + been + Ved/V3 + (by O)}$

`26.` Alan hasn't visited his parents for ages

Giải thích: $\text{S + have/has + Ved/V3 + ...}$

`27.` It hasn't rained here for a fortnight.

Giải thích: $\text{S + have/has not + Ved/V3 + ...}$

`28.` Never in my life have I seen such a mess.

Giải thích: $\text{Never + trợ đt + S + V + O}$

`29.` It's over a year since I was able to see them

Giải thích: $\text{It is + ...+ since + S + V}$

`30.` It is 20 years since John and Mary moved to Edinburgh.

Giải thích: $\text{It is + ...+ since + S + V}$

$chucbanhoctot$

$#thaonguyeneakar$