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.

they both go up but then go back down. they both end lower than they started. lastly, they both are competitive/the second on.

explanation:

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.