`1`. turn → turning

`⇒` Cấu trúc: After + Ving

`⇒` Công thức: Giới từ + Ving

`2`. it → ∅

`⇒` Which thay cho a festival

`⇒` Không cần it nữa

`3`. celebrate → celebrated

`⇒` Cấu trúc: S + should be + Vpp: ai đó nên được làm gì

1. After turn off the lights, she closed the door and the window.

→ After turning off the lights, she closed the door and window.

2. Tet is a festival which it occurs in late January or early February.

→ Tet is a festival occurs  in late January or early February.

3. I think mother's day should be celebrate in our country.

→ I think mother's day should be celebrated in our country.

                                                                                                 @anhsadgirl