— 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
网友回答
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。