Refer to the Diagram, Which Shows Demand and Supply Conditions

Refer to the diagram, which shows demand and supply conditions in the competitive market for product X. Other things equal, a shift of the supply curve from S0 to S1 might be caused by a(n)

A) increase in the wage rates paid to laborers employed in the production of X.
B) government subsidy per unit of output paid to firms producing X.
C) decline in the price of the basic raw material used in producing X.
D) increase in the number of firms producing X.