What type of smoke screen provides a thick, vertical barrier between enemy and friendly troops?

The answer is a smoke curtain. It is a dense, vertical development of smoke. It is positioned between friendly and enemy positions to avert or damage enemy ground observation of friendly positions. Since the smoke curtain is not placed directly on friendly troops, it will not hinder friendly operations. Also, it activates in the event of a fire, on condition that a means of diverting smoke away from a preferred location or protecting an area from direct smoke infiltration.

i think the answer is

mass

your answer should be c) enjoy!