You performed the RMAN database backup having a backupset key number 231 with the KEEP FOREVER option. After some days, you want to change the status of the database backup and you issued the following command: RMAN>CHANGE BACKUPSET 231 NOKEEP; What is the implication of this command?（）

• A、The backup is deleted.
• B、The backup is marked unavailable.
• C、The backup overrides the backup retention policy.
• D、the backup becomes eligible for deletion according to the existing retention policy