Question

Jack _______ swim when he was five years old.

A．can

B．could

C．may

D．must

Answer 1

B

词义辨析。Can，could能，会；may可以；must必须。句意：杰克5岁时会游泳。排除C,D；根据when he was five years old，可知要用一般过去时，所以选B ，could，表过去能够。