The function below models the correlation between the number of hours a plant is kept in sunlight (x) and the height (y), in mm, to which it grows: y = 4 + 2x what does the slope of this function represent? a. the original height of the plant was four mm. b. the original height of the plant was two mm. c. the height of the plant increases by two mm for every hour of sunlight it receives. d. the height of the plant increases by four mm for every hour of sunlight it receives.