To allow a regular user account to mount and unmount a filesystem (for instance, a cdrom or floppy), which option need to be added to the corresponding line in /etc/fstab?

`nouidchk` is an obscure option related to NFS mounts and UIDs, not for general user mounting permissions.

`alluser` is not a standard `fstab` mount option.

C is correct because the `user` option, when added to an `/etc/fstab` entry, allows any regular user (not just root) to mount and unmount the corresponding filesystem. This is commonly used for removable media devices like CD-ROMs or USB drives, simplifying their management for non-administrative users.

`auto` causes the filesystem to be mounted automatically at boot time or when `mount -a` is run, but does not grant regular users mount/unmount privileges.