Believe it or not, the best answer is "D". At night, movement is the first thing a sentry notices when a flare burst into flame. If you freeze you appear to be part of the landscape, but a sentry will notice even the slightest movement and bullets and shells will start flying towards you. When a flare bursts open - freeze!

Night warfare was terrifying. The darkness could hide friends, enemies, barbed wire, . . . anything. It was easy for a soldier to lose his way and end up in great danger. The flares, shells and tracer bullets added to the confusion. Here is a recreation of a night time battle from the film "Legends of the Fall":"