I'm busy working=I'm busy in working. 也就是说,working是动名词,充当宾语。类似:I spent two days (in) finishing the work.I had no trouble (in) finding his house.本句结构就是这样:忙于做某事的意思这个busy与后面的词是没有修饰关系的。I am busy我很忙I am busy working.我忙于工作。He is busy writing something.他在忙于写东西。He is busy with some important things,...