A.failure when no standby database is configured
B.failure because a data file is renamed accidentally
C.failure that requires no archive logs to be applied for recovery
D.failure due to loss of connectivity-for example， an unplugged disk cable

A.Back up the Flash Recovery Area.
B.Decrease the retention time for the database backup and flashback log files.
C.Manually delete all the archived log files from the Flash Recovery Area by using operating system （OS）commands.
D.Manually delete all the expired backup sets from the Flash Recovery Area by using operating system（OS） commands.