按键电话机可分为哪几大系统？

A. 正确
B. 错误

A. The leaf blocks in the index are doubly linked.
B. The leaf node stores a bitmap for each key value.
C. The rows with NULL value in key columns also have entries in the index.
D. The deletion of a row from the table causes a logical deletion in index leaf block and the space becomes available for the new leaf entry.

A. 公安机关
B. 治安机构
C. 金融管理办公室
D. 网管

A. 以消为主
B. 以防为主
C. 以人为主