Listen! The birdin the tree.A. singB. singingC. is singingD. is sing.

问题补充：

Listen! The birdin the tree.

A. sing

B. singing

C. is singing

D. is sing.

答案：

A. sing

B. singing

(答案→)C. is singing

D. is sing.

解析：本题考查时态。根据listen，可知用现在进行时。句意：听！小鸟正在树上唱歌。