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 grou