When I walked past his house I heard him .A. to singB. sang C. singsD. singing

问题补充：

When I walked past his house, I heard him .

A. to sing

B. sang

C. sings

D. singing

答案：

A. to sing

B. sang

C. sings

(答案→)D. singing

解析：此题考查固定举行结构hear sb do sth和hear sb doing sth之间的区别，前者表示听到某人经常做某事或做过某事，后者表示听到某人正在做某事。根据语境提供的信息可知我听到他正在唱歌，故选D。