View the Exhibit to examine the output for the CROSSCHECK BACKUP command.
Which statement is true about the output of the command? 
A. The backup piece is expired as the new backup is available
B. The backup piece is expired because the operating-system file was not found
C. The backup piece is expired because the retention period for the backup has expired
D. The backup piece is expired because the backup set to which it belongs is not complete
CROSSCHECK BACKUP 的作用是检查备份的可用性（物理上是否存在），并对失效的备份集打上 expired 标记
ACD 都属于违背备份策略的备份集，需要使用 obsolete 操作 。