The correct answer is B, as the Viet Cong forces were constantly on the move because they tried to avoid US troops and bombers.
The Viet Cong carried out guerrilla war tactics, mobilizing through subterranean tunnels in the middle of the jungle. In this way, it was easy for them to appear and disappear in a matter of minutes, so their attacks were sudden and difficult to predict by the American forces.
For the Viet Cong this meant a double advantage, the surprise factor that added to the knowledge they had of the terrain where they fought, and also the fact of being able to avoid the use of powerful American weapons by taking the fight to small spaces.
