The Graph Shown Depicts the Market for a Good

The graph shown depicts the market for a good. Assume the market was originally in equilibrium where the demand curve (D) and supply curve (S2) intersect. Something changes in the market, and the supply curve shifts to S1. What could have caused this shift?

A) The price of pizza sauce increased.
B) The price of pizza decreased.
C) The price of labor for pizza shops decreased.
D) Consumers no longer prefer to eat pizza.