单项选择题
A. Change the retention criteria.
B. Make the lost backup set pieces available to RMAN again.
C. Run the crosscheck command to correct the location for the backup set piece contained in the metadata.
D. Nothing. The backup set piece is lost forever.
E. Call Oracle support，their assistance is required.
单项选择题 Whatdoesitmeanifabackupisexpired？（）
多项选择题 Whywouldyourunthedeleteobsoletecommand？（）
单项选择题 You run the following commands： RMAN> list expired backup； RMAN> delete expired backup； What will happen to the backup set pieces associated with the backups that appear in the list expired backup command？（）