OCP 1Z0 053 153

153.You are managing an ASM instance. You previously issued the following statements: 
ALTER DISKGROUP dg1 DROP DISK disk2; 
ALTER DISKGROUP dg1 DROP DISK disk3; 
ALTER DISKGROUP dg1 DROP DISK disk5; 
You want to cancel the disk drops that are pending for the DG1 disk group. Which statement should you 
issue? 
A. ALTER DISKGROUP dg1 UNDROP disk2, disk3, disk5; 
B. ALTER DISKGROUP dg1 UNDROP; 
C. ALTER DISKGROUP dg1 UNDROP DISKS; 
D. You cannot cancel the pending disk drops. 
Answer: C 

http://docs.oracle.com/cd/E11882_01/server.112/e18951/asmdiskgrps.htm#OSTMG94118

Undropping Disks in Disk Groups

The UNDROP DISKS clause of the ALTER DISKGROUP statement enables you to cancel all pending drops of disks within disk groups. If a drop disk operation has completed, then this statement cannot be used to restore it. This statement cannot be used to restore disks that are being dropped as the result of a DROP DISKGROUP statement, or for disks that are being dropped using the FORCE clause.

The following example cancels the dropping of disks from disk group data1:

Example 4-8 Undropping disks in disk groups

ALTER DISKGROUP data1 UNDROP DISKS;