If a backup is expired， which of the following is true？（）  

• A、 It can never be used for a restore/recover operation.
• B、 Oracle will remove the backup set pieces from the flash recovery area.
• C、 The backup has been used at least once to restore and recover the database.
• D、 The backup is no longer valid because of a resetlogs operation.
• E、 The physical backup set pieces are missing from the media.