问题补充：
1.The student must hand in their compositions before school is over.改为被动语态
答案：
The students compositions must be handed in before school is over.
======以下答案可供参考======
供参考答案1:
The students compositions must be handed in before school is over.
供参考答案2:
the compositions must be handed in before school is over(by the students)
供参考答案3:
The students compositions must be handed in before school is over
