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 not a valid or recognized /etc/fstab mount option and has no effect on user mount permissions.

'alluser' is not a valid /etc/fstab option - the valid multi-user variant is 'users' (plural), which allows any user to unmount regardless of who mounted it.

Adding 'user' to the options field of an /etc/fstab entry allows any non-root user to execute mount and umount on that specific device. This is commonly used for removable media like cdroms or floppies so desktop users can manage them without sudo. The 'user' option also implies 'noexec', 'nosuid', and 'nodev' by default for security.

'auto' controls whether the filesystem is mounted automatically at boot time and has nothing to do with which user accounts can mount it.