The correct answer is (C) A camp, usually improvised for brief use; a temporary camp without tents, or with only pup tents; a makeshift shelter. Also, a military encampment made with tents or improvised shelters. Finally, a place used for such an encampment.

Bivouac comes from German beiwacht (an additional night watch), beiwaccht, biwache

Examples of use:

• They chose a suitable spot for a bivouac about an hour before sunset.
• We continued to drive for some time to be certain to avoid the army bivouac.