. Tom as well as his classmates a song when the teacher came into the classroom.A. are si

问题补充：

. Tom as well as his classmates a song when the teacher came into the classroom.

A. are singing

B. were singing

C. is singing

D. was singing

答案：

A. are singing

B. were singing

C. is singing

(答案→)D. was singing

解析：考查主谓一致。as well as连接两个主语时，谓语动词取决于前者，句意：当老师进入教室的时候，不仅汤姆的同学而且汤姆当时正在唱歌。根据语境表示过去某一时刻进行的动作应用过去进行时态，所以选D。