Which of the following phrases is TRUE regarding monitoring disk I/O with iostat？（）

• A、 The iostat can only be run as the root user
• B、 There could be zero percent I/O wait and still be an I/O bottleneck
• C、 Any I/O wait time displayed in output of "iostat" is an indication of severe I/O bottlenecks 
• D、 Running "iostat" without any arguments/parameters is sufficient for resolving I/O bottlenecks