Where Is the Opposed Air Flow Method of Smoke Control

Where is the opposed air flow method of smoke control typically used?

A) Areas with existing barriers, such as stairwells with doors or HVAC ductwork with dampers.
B) Within the smoke control station, or other areas where the air flow will dilute the concentration of smoke.
C) Large spaces where smoke migration is limited by opposed air flow, such as subway and railroad tunnels.
D) Large spaces were the smoke can be maintained at a level of 6 to 10 feet (2 m to 3 m) above the highest occupied floor.