Answer :

`->`They haven't celebrated a harvest festival for two years.

`->`The last time they celebrated a harvest festival was two years ago.

`->`They last celebrated a harvest festival two years ago.

`@`Form :

S + last + V2/ed + time ( thời gian trong quá khứ )

`=`S + have/has not + Vpp + since/for + time

`=`It’s + time + since + S ( last ) + V2/ed

`=`The last time + S + V2/ed + was + time

Ans:

`@` They haven't celebrated a harvest festival for two years.

`@` They last celebrated a harvest festival two years ago.

`@` The last time they celebrated a harvest festival was two years ago.

`-` Cấu trúc chuyển đổi  quá khứ đơn `-` hiện tại hoàn thành.

`<=>` It + be + time + since + S + V(quá khứ) + O.

`<=>` S + have/has + not + V3/Vpp + O + time.

`<=>` S + last + V(quá khứ) + O + time.

`<=>` The last time + S + V(quá khứ) + O + be + time.