Listen! Someone in the next room.A. singB. singingC. is singingD. are singing

问题补充：

Listen! Someone in the next room.

A. sing

B. singing

C. is singing

D. are singing

答案：

A. sing

B. singing

(答案→)C. is singing

D. are singing

解析：根据语境可知此句的含义是;听，有人在隔壁正在唱歌，考查的是现在进行时的基本用法。Someone做主语是谓语动词常用单数形式，故选C。