After performing a clean shut down of the database instance for maintenance, you mount thedatabase and then execute a command to open the database: SQL> ALTER DATABASE OPEN;  Which two statements are true()
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
出自:Oracle认证