1. The last time he wrote to me was in April

-> The last time + S + V2/ed + was in time

= S + have/has + not + V3/ed + since time

2. She last had a swim five years ago

-> S + last + V2/ed + time ago

3. They haven't talked to each other for two months

-> S + have/has + not + V3/ed + for time

4. She hasn't seen her elder sister since 1999

-> The last time + S + V2/ed + was in time

= S + have/has + not + V3/ed + since time

5. It's years since she last wrote to me

-> S + have/has + not + V3/ed + for time

= S + time + since + S + last + V2/ed

6. It's ten years since Robert and Catherine were married

-> It's + time + since + S + (last) + V2/ed

1) He has not written to me since April. 
=> The last time he wrote to me was in April.

2) She hasn't had a swim for five years
=> She last had a swim five years ago.
3) They last talked to each other two months ago
=> They haven't talked to each other for two months.
4) The last time she saw her elder sister was in 1999
=>She hasn't seen her elder sister since 1999.
5) She hasn't written to me for years
=> It's years since she last wrote to me.
6) Robert and Catherine have been married for ten years.
=> It's ten years since Robert and Catherine were maried.

S + have/has + not + V3 + for + khoảng thời gian/since + thời gian đã được xác định.

→The last time + S + V(quá khứ) + was + thời gian + ago/last + thời gian.

→S + last + V(quá khứ) + thời gian + ago/last + thời gian.

S + have/has + V3 + for + khoảng thời gian/since + thời gian đã được xác định.

→It's + thời gian + since + S + last + V(quá khứ)/the last time S + V(quá khứ).