The application workload on your database is same between 10 a.m. and 11 a.m. on weekdays. Suddenly you observe poor performance between 10 a.m. and 11 a.m. in the middle of the week. How would you identify the changes in configuration settings， workload profile，and statistics to diagnose the possible causes of the performance degradation？（）

A.Set the STATISTICS_LEVEL initialization parameter to ALL.
B.Create a baseline on a pair of snapshots that have the statistics of the peak­load period in the database.
C.Decrease the snapshot interval in the AWR to collect more number of snapshots during the peak­load period.
D.Set the snapshot retention period in the Automatic Workload Repository （AWR） to zero to avoid theautomatic purging of the snapshots.

A.The optimizer statistics are collected automatically.
B.Only the timed operating system （OS） statistics and plan execution statistics are collected.
C.The Oracle server dynamically generates the necessary statistics on tables as part of query optimization.
D.The snapshots for the Automatic Workload Repository （AWR） are not generated automatically. 
E.Snapshots cannot be collected manually by using DBMS_WORKLOAD_REPOSITORY PACKAGE.

A.when performing export and import using Oracle Data Pump
B.when performing backup and recovery operations using Oracle Recovery Manager
C.when performing batch processing and bulk loading operation in a data warehouse environment 
D.in an online transaction processing （OLTP） system where large number of client sessions are idle most of the time