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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.

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出自：Oracle认证

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