Passage A  Toys play an essential part in many people’s childhood. Some of our best memories even come from times spent happily__16__ toys. We may wonder why children like toys and why parents are willing to spend money on their children’s toys.__17__, toys allow children to learn how the world works, not only the physical one, but also the social one. Of course,children do not sense they are learning about __18__ when they find it easy to stack blocks but impossible to stack balls.Besides, while children are playing board games with their friends, they are also learning how to __19__ socially. Important asthey are, toys do not have to be fun because children’s imagination can __20__. Their fun is really all in the mind.
16.
(A) playing
(B) playing with
(C) to play
(D) to play with