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 = 2 + 4x
What does the y-intercept of this function represent?

A. The original height of the plant was 4 mm.

B. The original height of the plant was 2 mm.

C. The height of the plant increases by 2 mm for every hour of sunlight it receives.

D. The height of the plant increases by 4 mm for every hour of sunlight it receives.