You observe that database performance has degraded over a period of time. While investigating the reason， you find that the size of the database buffer cache is not large enough to cache all the needed data blocks.  Which advisory component would you refer to， in order to determine the required size of the database buffer cache？（） 

• A、Memory Advisor
• B、Segment Advisor
• C、SQL Tuning Advisor
• D、SQL Access Advisor
• E、Automatic Database Diagnostic Monitor （ADDM）