The first thing she usually does ______ arriving home is to open the windows镜子and air the room.
问题描述：
The first thing she usually does ______ arriving home is to open the windows镜子and air the room.
A.by B.with C.in D.on
标准答案选D,为什么?
答
on作介词,表示在……的时候,一……就