A. Put the database in hot backup mode and perform an online backup，including backing up the  archived redo logs.
B. Just back up the database datafiles without shutting down the database.
C. You will have to wait until you can shut down the database to perform the backup.
D. Mark each datafile as backup in progress， back them up individually，and then mark them as backup not in progress. No archived redo logs will need to be backed up.
E. Only back up the datafiles that the user will not be touching. Once the user has finished what they were doing，you can shut down the database and back up the datafiles the user changed during the  course of the remaining backup

A. The DGROUP1 disk group was unmounted by another DBA.
B. A datafile has been lost， causing the ASM disk group DGROUP1 to go into the DISMOUNTED state
C. One of the redundant disks （DGROUP1） has been lost in a disk group.
D. This query has no meaning in an ASM instance.
E. A disk associated with a disk group was discovered after the ASM instance initially opened.