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