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
原文：http://www.cnblogs.com/Babylon/p/7843869.html