He was often seen____basketball on the playgroundA play Bis played Cto play Dplaying
问题描述：
He was often seen____basketball on the playground
A play Bis played Cto play Dplaying
答
playing
see sb do 看见全过程
see sb doing 只是看见，没有全过程。
答
D,playing,see sb doing的被动式,People often saw him playing basketball on the playground