An officer of the Federal force, who in a spirit of adventure or in quest of knowledge had left the hidden bivouac in the valley, and with aimless feet had made his way to the lower edge of a small open space near the foot of the cliff, was considering what he had to gain by pushing his exploration further." from "A Horseman in the Sky" by Ambrose Bierce What is the best definition of bivouac in this sentence? A. patrolling B. projecting part C. infantryman; soldier D. military encampment