What Is the Purpose of a System Mount Unit

What is the purpose of a system mount unit?

A) It is used by the command systemd-mount and allows users to mount partitions to mount points of their choice It is used by the command systemd-mount and allows users to mount partitions to mount points of their choice
B) It is used only to mount network file systems to local mount points. It cannot be used for local media
C) It is created by the command systemd-fstab-generator to integrate entries from /etc/fstab into the system boot process It is created by the command systemd-fstab-generator to integrate entries from /etc/fstab into the system boot process
D) It is used by the command mount when using system to mount and unmount file systems mount when using system to mount and unmount file systems