How can you reverse the effects of an ALTER DISKGROUP … DROP DISK command if it has already completed?

How can you reverse the effects of an ALTER DISKGROUP … DROP DISK command if it has already 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.

Explanation:
Use the undrop_disk_clause cancel the drop of disks from the disk group. This clause is not relevant for disks that have already been completely dropped from the disk group or for disk groups that have been completely dropped.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_1006.htm#i2168780
Use the CREATE DISKGROUP clause to create a collection of disks.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_5008.htm
Use the add_disk_clause to add one or more disks to the disk group and specify attributes for the newly added disk.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_1006.htm#i2168780