What file should you edit to change the default background for it?

You have just set up the X Display Manager as your default display manager. What file should you edit to change the default background for it?

A.
/etc/X11/prefdm

B.
/etc/X11/xdm.conf

C.
/etc/X11/xdm/Xsetup

D.
/etc/X11/xorg.conf