A senior executive asked an administrator to change the default background of the executive's machine, which uses XDM. Which of the following files would the administrator edit to achieve this?

The `/etc/X11/xdm/Xsetup` script is executed by XDM before the login screen appears and before any X server is started for a display. It is the appropriate place to define system-wide settings that affect the X server environment for the login display, such as setting the root window background or starting other display-related programs.

`/etc/X11/xdm.conf` (or commonly `xdm-config`) is the main configuration file for XDM, defining paths and other general operational settings, but it does not contain the script for setting the display background.

`/etc/X11/xdm/Defaults` usually contains default Xresources settings for XDM, which define font sizes, colors, and other visual aspects of X applications, not a script for setting the root window background.

`/etc/X11/defaults.conf` is not a standard XDM configuration file location for setting display backgrounds; this filename is not part of typical XDM configurations.