As we inhale air, oxygen enters the respiratory system and the circulatory system to transport it to the other parts of the body and to all cells. As the oxygen is already transported, the blood becomes deoxygenated and carries a CO2 which returns to the lungs and then we exhale the carbon dioxide.
I'd go with the third one because the products of both of them are oxygen and carbon dioxide.
Fog begins to form when water vapor condenses into tiny liquid water droplets that are suspended in the air.
