The Figure Given Below Shows the Demand and Supply Curves

The figure given below shows the demand and supply curves of automobiles.Figure 13.3
In the figure,
D: Demand curve of automobiles
S: Supply of automobiles prior to the tax
S+t: Supply of automobiles after the tax

-Suppose that the current price of a marketable permit to emit one ton of gunk is $60. For firm A, the marginal cost of reducing one ton of gunk is $50. For firm B, the marginal cost of reducing one ton of gunk is $70. Under a marketable permit system, _____.

A) both firms will buy a permit and emit one more ton of gunk
B) firm A will buy a permit and emit one more ton of gunk, whereas firm B will reduce its emissions of gunk by one ton
C) firm B will buy a permit and emit one more ton of gunk, whereas firm A will reduce its emissions of gunk by one ton
D) both firms will reduce their emissions of gunk by one ton
E) both firms will go out of business