You have specified the warning and critical threshold values of an application tablespace to be 60% and 70%， respectively. From the tablespace space usage metrics， you find that the actual space usage has reached the specified warning threshold value， but no alerts have been generated. What could be the reason for this？（）

• A、The EVENT parameter was not set.
• B、The SQL_TRACE parameter is set to FALSE
• C、The Enterprise Manager Grid Control is not used.
• D、The STATISTICS_LEVEL parameter is set to BASIC
• E、The TIMED_STATISTICS parameter is set to FALSE