053-573

Upon starting your database, you receive the following error:
SQL> startup ORACLE instance started.
Total System Global Area 171581440 bytes Fixed Size 1298640 bytes Variable Size 146804528 bytes Database Buffers 20971520 bytes Redo Buffers 2506752 bytes Database mounted.
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1: '/oracle01/oradata/orcl/redo01.log' ORA-00312: online log 1 thread 1:'/oracle01/oradata/orcl/redo01a.log'
You can choose from the following steps:
Which is the correct order of these steps in this case?
A. Restore the database datafiles.
B. Issue the alter database clear unarchived logfile group 1 command.
C. Issue the alter database open command.
D. Issue the alter database open resetlogs command.
E. Recover the database using point-in-time recovery.
F. Issue the Startup Mount command to mount the database.
G. Back up the database.
A. a, f, e, d, g
B. f, e, d
C. f, b, c, g
D. a, f, c
E. The database cannot be recovered.

　　ORA-00312 or ORA-00313 http://www.linuxidc.com/Linux/2012-02/53426.htm
　　挂载(mount)→清理(clear)→打开(open)→备份(backup)
　　You should first start the database in mount mode using the startup mount command.You then issue the alter database clear unarchived logfile command.This will clear the log file if it needs to be archived and re-create the onlie redo log group.If that command is successful,then you issue the alter database open command.The last step,backing up the database,is very important since your previous backup will not be able to recover the database beyond the point of the cleared redo sequence number.This is because you have skipped a redo log in the redo log stream.