1. Mai/ go/ school/ on time/ if/ she/ had/ alarm clock.

`->` Mai would go to school on time if she had an alarm clock.

Câu điều kiện loại 2: S + Ved + O, S + would/could/might + V + O

2. It/be/ necessary/ protect/ environment.

`->` It is necessary to protect the environment. 

It is adj ( for sb ) to V: Thật là.... cho ai đó....để làm gì

3. They/ not see/ each other/ since/ they/ leave school.

`->` They have not seen each other since they left school

4. My mother/ enjoy/ watch movies/ which/ from/ Korea.

`->` My mother enjoys watching movies which are from Korea

1. Mai would go to school on time if she had an alarm clock.

2. It is necessary to protect environment

3. They haven't seen each other since they left school

4. My mother enjoys watching movies which are from Korea