On a machine running several X servers, how are the different instances of the X11 server identified?

A. By a fixed UUID that is defined in the X11 configuration file.

B. By a unique IPv6 address from the fe80::/64 subnet.

C. By the name of the user that runs the X server like x11:bob.

D. By a device name like /dev/X11/xservers/1.

E. By a display name like:1.