Đáp án:

`28,` How long is it since he wrote to you?

- When + did + S + V ? `=` How long is it + since + S + V2 / V-ed ?

- Dịch: Đã bao lâu rồi kể từ khi anh ấy viết thư cho bạn?

`29,` I've worked for this company for a year.

- S + started / began + to V / Ving + time trong QK.

`=`S + have / has + V3 / PII + for + khoảng thời gian / since + mốc thời gian

- Dịch: Tôi đã làm việc cho công ty này trong một năm.

`30,` 

$→$ Jack has taught English for `10` years.

$→$ It is `10` years since Jack began teaching English.

- S + started / began + to V / Ving + time trong QK.

$→$ S + have / has + V3 / PII + for + khoảng thời gian / since + mốc thời gian

$→$ It is + time + since + S + V2 / V-ed.