Which of the following commands is used to enforce checking of a file system even if the file system seems to be clean?

The -f (force) option instructs e2fsck to perform a complete check of an ext2/ext3/ext4 filesystem regardless of whether the superblock indicates the filesystem was cleanly unmounted. Without -f, e2fsck exits immediately on a clean filesystem; the -f flag overrides this skip behavior and runs the full integrity check unconditionally.

e2fsck -p runs the utility in automatic preen mode, which repairs only safe, non-destructive errors without user prompting, but does not force a check on a filesystem already marked as clean.

e2fsck -b specifies an alternative superblock to use when the primary superblock is damaged or unreadable, and does not affect whether a clean filesystem is checked.

e2fsck -c invokes the badblocks program to scan for bad sectors on the underlying device, which is a separate hardware-level test rather than a forced filesystem integrity check.