play on the "sand"还是"sands"?为什么?

play on the sand还是sands?为什么? play on the skate 还是play skate? play on the competitions 还是play on the stages 玩电脑是play on the computer 还是play computer Jack had a good time____with sand on the beach.A,to play B,of playing C,play D,playing.答案选哪个,为什么? play computer还是play the computer还是play on the computer The boy draws on the sand ____thin sticks or stones. play on the beach play on the i can play the computer还是 i can play on the computer?如题 请问是play on the team还是play for the team? sand前+an?There is a还是an “s”in the word“sand” Jack had a good time___with sand on the beach.A .to play B .of playing c .play D .playing答案是D.为什么?还有一个enjoy oneself 玩得很高兴后面是跟什么的 We see there are many marks of another man's feet ( ) A.to the sand. B.under the sand. C.on the sand. D.at the sands. let us play and to play sports on the playgroundlet us play and play sports on the playground还是let us play and to play sports on the playground There’re some children （ ）play on the ground.填playing还是play the boy's father built them a large sand box in which to play如何翻译 提问一道英语题：The children are playing on ( ).1.the sand 2.a sand 3.the sands 4.sand正确答案选择3,这是为什么呢?sand不是沙滩的意思吗?应该是不可数的呀?