Examine the following ALTER command:
SQL> ALTER DISKGROUP dgroup1 UNDROP DISKS;
What is the purpose of the command?
A. It cancels all pending disk drops within the disk group.
B. It restores disks that are being dropped as the result of a DROP DISKGROUP operation
C. It mounts disks in the disk group for which the drop-disk operation has already been co pleted
D. It restores all the dropped disks in the disk group for which the drop-disk operation has already been completed
E. It adds previously dropped disks back into the disk group
此题考点是磁盘组 undrop 选项的用法，使用这个选项可以取消正在从磁盘组删除的磁盘。通过指定磁盘组名称或者使用 ALL 子句，来取消那些准备删除的磁盘组。
这个选项不会关联那些已经被删除的磁盘或磁盘组。这个操作是一个长时间的操作，可以通过V$ASM_OPERATION 视图查询 ASM 操作的详细信息。