How do you konw that she likes singing?I often hear her---（s

填sing是对的.
这是hear sb do sth 句型,”听见某人做某事“.感官动词hear / listen to / see / look at / watch / notice / observe +sb +do sth
如果要用三单,则hear后面要用宾语从句,即：I often hear （ that） she sings after class.
【俊狼猎英】团队