_____arriving home,he saw the letter behind the door on the floor.A.Over B.In C.Upon D.At答案为什么是C,不能是D?

分类: 作业答案 • 2022-01-02 15:22:44

问题描述：

_____arriving home,he saw the letter behind the door on the floor.
A.Over B.In C.Upon D.At
答案为什么是C,不能是D?

答

C
on/upon doing 一怎么样
固定搭配
）