单项选择题 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？（）

多项选择题 You are performing a block media recovery on the tools01.dbf data file in the SALES database by using RMAN.   Which two statements are correct in this scenario？（）

单项选择题 Your database is open and running in ARCHIVELOG mode. You take RMAN full backups every Sunday night. On Monday morning， while querying the user1.employees table， you receive the following error message：  01578： ORACLE data block corrupted （file # 5， block # 51） ORA-01110： data file 5：  ’/u01/app/oracle/oradata/orcl/example01.dbf’  You need to rectify the corruption while ensuring the following： The data file should remain online.  The mean time to recover （MTTR） should be minimal.  You are not using a backup control file， and all the archived logs are accessible.   Which option would you choose？（）