What does the command mount -a do?

It ensures that all file systems listed with the option noauto in /etc/fstab are mounted.

It shows all mounted file systems that have been automatically mounted.

It opens an editor with root privileges and loads /etc/fstab for editing.

It ensures that all file systems listed with the option auto in /etc/fstab are mounted.

It ensures that all file systems listed in /etc/fstab are mounted regardless of their options.