单项选择题
Oracle Net Services is composed of several communication layers， known as a stack，which enables clients and database severs to share，modify，and manipulate data. Which reveals the correct architecture，in hierarchical order，of the client-side stack？（）
A.A B.B C.C D.D
单项选择题 WhichstatementistrueregardingRMANcomponents？（）
单项选择题 You issue this statement：ALTER DATABASE BACKUP CONTROLFILE TO TRACE； What does the statement generate？（）
单项选择题 Whichstatementistrueregardingcheckpointsandrecovery？（）
