1. The last time she came back to her hometown was 4 years ago.

=> She hasn't come back  to her hometown  for 4 years.

The last time+S+Vqkđ= S+ has/have+ not+ PII

2. He started working as a bank clerk 3 months ago.

=> He has worked as a bank clerk for 3 months .

S+ started+ Ving= S+has/have+ PII

3. It has been 5 years since we first flew to Singapore.

=> We have flown to Singapore for 5 years.

It has been+ time+ since+ S+ Vqkđ= S has/have+ PII+ for+ khoảng tgian

4. I last had my hair cut in November.

=> I haven't had my hair cut in November.

S+ last+ Vqkđ= Shas/have+ not+ PII

5. The last time we called each other was 5 months ago.

=> We haven't called each other for 5 months.

The last time+S+Vqkđ= S+ has/have+ not+ PII

6. It is a long time since we last met.

=> We haven't met for a long time.

It is a long time since+ S+ last+Vqkđ= S+ has/have+ not+ PII

7. When did you have it?

=> How long have your had it?

When+ did+S+V?= How long+ have+ S+PII?