Timothy bought a plant for his yard. He uses the expression 56 +20x to estimate the height of the plant after x years. Which statement explains the meaning of the coefficient 20?
A. It is the estimated increase in height per year.
B. It is the estimated increase in height after x years.

C. It is the estimated height of the plant after x years.
D. It is the height of the plant when Timothy bought it.
E. It is the height of the plant when Timothy last measured it.