SQL语言的GRANT和REVOKE语句主要用来维护数据库的( )
A．安全性
B．完整性
C．可靠性
D．一致性
参考答案：A
—What do you often do after school?
—I ______ basketball with my friends.[ ]
A. play
B. played
C. will play
D. are playing
下面四幅图中，属于北半球的中高纬度的环流的是（ ）
