Which file would you edit to achieve this?

Your senior administrator asked you to change the default of his machine, which uses XDM (X Display Manager).
Which file would you edit to achieve this?

A.
/etc/X11/xdm/Xsetup

B.
/etc/X11/xdm.conf

C.
/etc/X11/defaults.conf

D.
/etc/X11/xdm/Defaults