You are maintaining your OLTP database in Oracle10g. While observing the performance of the database， you find that the log switch occurs more than once for every 20 minutes， affecting the database performance. Which factor is responsible for frequent log switches？（）  

• A、the value of the UNDO_RETENTION initialization parameter
• B、the value of the optimal redo log file size provided by the Redo Logfile Size Advisor
• C、the online redo log files size
• D、the number of redo log members in a group