题目

 —Why didn't you try your best to get on the subway? —I tried to, but it started moving_________I could get on it. A. before       B. after       C. since           D. if 答案：A已知集合，Ｒ是实数集，则 ＝（　　） A．　　   　B．　　　  Ｃ．　　 　Ｄ．以上都不对