You are using an application that you want to appear on the screen of another machine.

What environment variable would you have to set or edit to achieve this?

A.
DISPLAY

B.
REMOTE

C.
REMOTE_XWINDOW

D.
SCREEN

Explanation:
From http://www.xfree86.org/current/X.7.html#sect4:
On POSIX systems, the default display name is stored in your DISPLAY environment variable. This variable is set automatically by the xterm terminal emulator. However, when you log into another machine on a network, you will need to set DISPLAY by hand to point to your display.