The radar control that shortens all echoes on the display and reduces clutter caused by rain or snow is the __________.

Correct Answer: Option B — fast time constant (differentiator)

The Fast Time Constant (FTC) control is specifically designed to reduce clutter caused by rain, snow, or sea return. It functions by differentiating the video signal, which shortens the pulse length of the echoes on the display, thereby reducing the size of clutter patches and improving target detection in adverse weather.