the teacher didn't sit down until he saw every student already had a chair____
问题描述：
the teacher didn't sit down until he saw every student already had a chair____
A to sit B to sit down C to sit at D to sit on
原因是什么呢 其他选择为什么不能选
答
have a chair to sit on.这里考的是介词.sit on a chair.用on才对.