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