单项选择题 Evaluate the following function code：   CREATE FUNCTION get_dept_avg（dept_id NUMBER） RETURN NUMBER RESULT_CACHE RELIES_ON （EMPLOYEES） IS avgsal NUMBER（6）； BEGIN  SELECT AVG（SALARY）INTO avgsal FROM EMPLOYEES   WHERE DEPARTMENT_ID = dept_id； RETURN avgsal； END get_dept_avg；   Which statement is true regarding the above function？（）

单项选择题 You want to use RMAN to create compressed backups.  Which statement is true about the compression algorithms that RMAN can use？（）

单项选择题 You have the following requirements in relation to the detection of block corruption for your database instance：   Check for logical self-consistency of data blocks when modified in memory.  Checksums are calculated before and after the block change.  Checks are performed for the lost writes to the physical standby database.   Which method would help you perform the above checks automatically？（）