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