The df command indicates that a filesystem is full， however， the du command indicates that not all space is allocated.  How would the system administrator isolate the discrepancy（）

• A、Use the fuser command to identify deleted but open files.
• B、Use the ipcs command to view orphan shared memory segments.
• C、Use the defrag command to determine if the filesystem is fragmented.
• D、Use the topas command to identify processes using the most system resources.