What Does the Term "Outside Air"refer To, When Used in the Context

Multiple Choice

What does the term "outside air"refer to, when used in the context of a ventilation system?

A) the air outside the building
B) the amount of air that we need to add to the ventilation system to replace air that has been used in the system
C) the air when it is not inside the ventilation system
D) factors other than air in the ventilation system