How can you reverse the effects of an ALTER DISKGROUP ... DROP DISK command if it has not yet completed?()  
A: Issue the ALTER DISKGROUP ... ADD DISK command.
B: Issue the ALTER DISKGROUP ... UNDROP DISKS command.
C: Issue the ALTER DISKGROUP ... DROP DISK CANCEL command.
D: Retrieve the disk from the Recycle Bin after the operation completes.
出自:Oracle认证