题干
Look, so many passengers _________ with their smart phones on the underground.
A：played
B：will play
C：are playing
D：have played
答案(点此获取答案解析）
C
Look, so many passengers _________ with their smart phones on the underground.
A：played
B：will play
C：are playing
D：have played
，全集
，则集合 
中的元素共有 ( )