1. He has never visited Ha Long Bay before.

2. She has worked here since last year.

3. We have eaten lunch since it started to rain.

4. I haven't had my hair cut since she left me.

5. He hasn't met me for 5 months.

6. We haven't met for a long time.

1. He has never visited Ha Long Bay before.

`->` This is the first time + S + have/has + Vpp = S + have/has + never + Vpp + before.

2. She has worked here since last year.

`->` S + started + to V/ Ving + thời gian = S + have/has + Vpp + since + mốc thời gian 

3. We have eaten lunch since it started to rain.

`->` S + began + to V/ Ving + when + S2 + V2/ed = S + have/has + Vpp + since + S2 + V2/ed

4. I haven't had my hair cut since she left me.

`->` S + last + V2/ed + when + S2 + V2/ed = S + have/has + Vpp + since + S + V2/ed

5. He hasn't met me for 5 months.

`->` The last time + S + V2/ed + was + thời gian + ago = S + have/has + not + Vpp + for + khoảng thời gian 

6. We haven't met ... for a long time.

`->` It + be + khoảng thời gian + since + S + last + V2/ed = S + have/has + not + Vpp + for + khoảng thời gian