The correct answer is: du.
du is a command-line utility for estimating file space usage. It can be used to list the disk usage of files and directories, or to calculate the total disk usage of a directory tree.
disk is a command-line utility for displaying information about disks and partitions. It can be used to list the disks and partitions on a system, or to display detailed information about a specific disk or partition.
fdisk is a command-line utility for partitioning disks. It can be used to create, delete, and resize partitions, or to change the type of a partition.
chkdsk is a command-line utility for checking the integrity of a disk. It can be used to scan a disk for errors, and to repair any errors that are found.
None of the above is not the correct answer.