Use the Following to Answer Question

Multiple Choice

Use the following to answer question:
Figure: Correcting for Market Failure
-(Figure: Correcting for Market Failure) Use Figure: Correcting for Market Failure.There is an external cost in the market illustrated in the figure,and the two upward-sloping lines reflect private and social marginal costs.If the government forces the private-sector firms to internalize any external costs:

A) the supply curve shifts to the right,from S₂ to S₁.
B) the supply curve shifts to the left,from S₁ to S₂.
C) the supply curve is unaffected.
D) price per unit decreases.