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