Play often as an activity for younger children is still important in the social develop

问题补充：

Play, often as an activity for younger children, is still important in the social development of teenagers.

A. to see

B. seeing

C. seen

D. to be seen

答案：

A. to see

B. seeing

C. seen

D. to be seen

解析：考查非谓语动词作定语。句意：玩，对小孩而言经常被视为一项活动，在青少年的社会性发展中仍然是重要的。Play与see之间为被动关系，故排除ＡＢ，不定式作定语表将来，根据句意，不符合题意，故排除。