A customer has a WebTrade application that initially uses the embedded LDAP to authenticate users. To enhance security, the customer decides to use OAM to authenticate some of the users against an external LDAP store. For this to work, a customer configured an OAMAuthenticator, but was not sure what to select for the Control Flag. What Control Flag should the customer choose?（） 

• A、OPTIONAL
• B、REQUISITE
• C、REQUIRED
• D、SUFFICIENT
• E、MANDATORY