问题补充：
The children are having a good time, with sand, others with toys．
A. some of them playing
B. some of them are playing
C. some of them
D. who playing
答案：
(答案→)A. some of them playing
B. some of them are playing
C. some of them
D. who playing
解析：可联系答.案.网客服索取。
