Don't open the door. There is a red sign of "Danger" on it.

--> Don't ...............................................

GIẢI THÍCH CẤU TRÚC GIÚP MÌNH LUÔN Ạ!!

They won't get high grades without good preparations. --> If they ..........

1. Shut up or I'll inform the teacher.

--> If ........

2. Never reach the shelf or I will punish you.

--> If .....................................

--> If you don't .....................

28. Polluted water can ...... do harm to people's health. (direct)