628.The database is running in the ARCHIVELOG mode. It has three redo log groups with one member

each. One of the redo log groups has become corrupted. You have issued the following command during

the recovery of a damaged redo log file:

ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;

Which action should you perform immediately after using this command?

A. You should perform a log switch

B. You should make a backup of the database

C. You should switch the database to the NONARCHIVELOG mode

D. You should shut down the database instance and perform a complete database recovery

Answer: B

答案解析：

ALTER DATABASE CLEAR UNARCHIVED LOGFILE GROUP 3;只用此命令，清除了日志组3，没有了联机重做日志，以前的备份就失效了，所有应该重新备份数据库。