（539）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.

答案：（A）

解析：

(ALTER DISKGROUP...DROP DISK的反操作就是添加磁盘ALTER DISKGROUP...ADD DISK)