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After performing a clean shut down of the database instance for maintenance, you mount the database and then execute a command to open the database:
SQL> ALTER DATABASE OPEN;
Which two statements are true? (Choose two.)
A.The online redo log files and online data files are opened.
B.All the online data file headers are checked for consistency.
C.Instance recovery is performed before opening the database.
D.The path and existence of all the log file members are checked.

　　打开数据库过程包括执行以下任务：
　　• 打开数据文件
　　• 打开联机重做日志文件
　　如果尝试打开数据库时任一数据文件或联机重做日志文件不存在，则 Oracle 服务器返回错误。
　　在最后这个阶段，Oracle 服务器会验证是否可以打开所有数据文件和联机重做日志文件，还会检查数据库的一致性。如有必要，系统监视器(SMON) 后台进程将启动实例恢复。