Which perquisite must be met before accomplishing the backup?

Examine the following RMAN command:
RMAN> CONFIGURE ENCRYPTION FOR DATABASE ON; RMAN> BACKUP DATABASE PLUS
ARCHIVELOG;

Which perquisite must be met before accomplishing the backup?

A.
Provide a password for the encryption.

B.
Set up an Oracle wallet for the encryption.

C.
No setup is required as it is a default encryption method.

D.
Both Oracle wallet and password must be set up for the encryption.

Explanation:
http://download.oracle.com/docs/cd/B28359_01/backup.111/b28270/rcmconfa.htm
To configure the environment so that all RMAN backups are encrypted:Set up the Oracle wallet as
explained in Oracle Database Advanced Security Administrator’s Guide.
Issue the following RMAN command:
CONFIGURE ENCRYPTION FOR DATABASE ON;
At this stage, all RMAN backup sets created by this database will use transparent encryption by
default