Correct answer choice is:
The Vietcong used guerrilla tactics.
They fought a guerrilla war, trapping American patrols, setting detonated traps and landmines, and planting bombs in cities. They merged in with the barbarians with normal standard garments. The Americans could not determine who the enemy was. Their maneuver was "hanging onto the belts" of the Americans - staying therefore near to the Americans so that they couldn't use air or artillery backup without paying the cost in the form of killing their own men.