An AIX system， which is running a database， is having performance issues with I/O writing.  The DBA has provided numbers for the HIGH and LOW watermarks for pending file writes， which will optimize the system for best performance.  To set these numbers， which of the following commands would be used？（）

• A、 perfmon -h 30 -l 25
• B、 chdev
• C、 no -o
• D、 smit chgsys