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（）
- AUse the fuser command to identify deleted but open files.
- BUse the ipcs command to view orphan shared memory segments.
- CUse the defrag command to determine if the filesystem is fragmented.
- DUse the topas command to identify processes using the most system resources.