Which two statements are true about a system? A: A system is a group of objects analyzed as one unit.
B: Energy that moves across system boundaries is conserved.
C: There’s only one way to define the boundaries of a system.
D: All systems are made by humans.

Assume that a person skiing high in the mountains at an altitude of h = 15100 ft takes in the same volume of air with each breath as she does while walking at sea level. determine the ratio of the mass of oxygen inhaled for each breath at this high altitude compared to that at sea level. assume that the air composition (i.e. % of air that is oxygen) is the same at sea level as it is at 15100 ft.