Temperature and oxygen level
Explanation:
They are opposites because they are the same chemical reaction but reversed. Cellular respiration takes glucose (from nutrient/food) and oxygen (from atmosphere) in order to make CO2 (think about exhaling) and H20 (water).
C.
The skeletal system provides structure to the human body.
B - When many individuals of the same species are available for mating.
And
C - When the individuals live in a stable environment in which they thrive.
