Chad decides to encrypt his existing Time Machine backup on an external disk. How should he proceed?

A.
Erase the disk using the Disk Utility then start a new Time Machine backup.

B.
Enable FileVault 2 on the startup disk to automatically encrypt the Time Machine backup.

C.
Get info on the Time Machine backup disk then select the “Enable encryption” checkbox.

D.
Use the Time Machine preferences to re-select the backup disk then select the “Encrypt backup disk checkbox.