问题补充：
We are having a math lesson now, you must stop music.
A. listen
B. to listen
C. listening to
D. for listening
答案：
A. listen
B. to listen
(答案→)C. listening to
D. for listening
解析：根据前文的内容We are having a math lesson now，可知说明应该stop doing sth，为停止做某事，故选C
