I look forward to their being challenged by the other students.为何用their?

问题描述:

I look forward to their being challenged by the other students.为何用their?
I look forward to their being challenged by the other students.
请问一下这边为什么要用 their

因为,look forward to 的to 是介词,因此,后面要跟名词
因此,be 的动名词是being,being challenged 是动名词的被动
名词前面自然有物主代词修饰,就是their