【题目】When Tom knocked at the door, I was busy ________ my homework and my brother was busy ________ a model plane.
A. to do; with B. doing; with doing
C. with; making D. with; to make
在线课程【答案】B
【解析】
试题分析：be busy with one's homework忙于做作业；be busy making a model plane忙于做飞机模型。