希望给出充分的理由说明see sb doing sth与see sb do sth的区别 1.——Do you often see William ___ on the playground? ——No,but he is often seen ___ Chinese Kungfu in the park. A.run;play B.run;to play C.running;play D.running;to play 2.I heard him ___ in the room almost every day. A.sing B.singing C.sings