We must pay attention to the teacher carefully in class.A. listenB. listening toC. hearD.

问题补充：

We must pay attention to the teacher carefully in class.

A. listen

B. listening to

C. hear

D. hearing

答案：

A. listen

(答案→)B. listening to

C. hear

D. hearing

解析：pay attention to注意，其后接动名词形式。listen to强调听的动作，hear强调听的结果。句意：我们在课上必须认真听老师的话。故选B。