Final answer:
The correct program segment to display the entire applet window red is option d.
Step-by-step explanation:
The correct program segment to display the entire applet window red is option d.
g.setColor(Color.red); sets the color of the Graphics object to red, and g.fillRect(0,0,800,600); fills the entire applet window with the specified color.
The other options either use the wrong method (drawRect instead of fillRect), or specify incorrect coordinates that would not cover the entire window.