Examine the code：   CREATE ROLE readonly IDENTIFIES USING app.chk_readwrite ； CREATE ROLE readwrite IDENTIFIED USING app.chk_readwrite ；   CREATE OR REPLACE PROCEDURE app.chk_readwrite  AUTHID CURRENT_USER IS  ipchk STRING（30）；  BEGIN  IF sys_context（‘USERENV’，’ISDBA’）=’TRUE’  THEN DBMS_SESSION.SET_ROLE‘READWRITE’） ；  ELSE DBMS_SESSION.SET_ROLE（‘READONLY’） ；  END； /   Which three statements correctly describe the Secure Application role definition？（）

• A、No user or application has to remember or hide a password. 
• B、It prevents everyone except a true DBA session from acquiring the READWRITE role. 
• C、app.chk_readwrite is called whenever a user tries to access rows protected by the READONLY or READWRITE label. 
• D、app.chk_readwrite is called by users or applications when they want to enable the READONLY or READWRITE role.