i heard him ()in the next room a few minutes ago.

这里的括号填的跟ago没关系,heard就是过去式.

这里是固定搭配：
Hear/see sb. do sth. 看见或听见某人做过或经常做
Hear/see sb. doing sth. 看见或听见某人正在做
Hear/see sb./sth. done 看见或听见某人被做,如 saw a thief caught yesterday

所以直接填sing