— What are the doing there?— They are busy their science experiment.A. Boys students; to

问题补充：

— What are the doing there?

— They are busy their science experiment.

A. Boys students; to do

B. Boy students; to do

C. Boys students; doing

D. Boy students; doing

答案：

A. Boys students; to do

B. Boy students; to do

C. Boys students; doing

(答案→)D. Boy students; doing

解析：考查名词复数和非谓语动词的用法。男学生的复数表示为boy students，固定结构“be busy doing sth”忙于做某事。