Suppose There Are Three Power-Generating Plants, Each of Which Has

Multiple Choice

Suppose there are three power-generating plants, each of which has access to 5 different production processes. The table below summarizes the cost of each production process and the corresponding number of tons of smoke emitted each.  
For all three firms, the marginal cost of pollution abatement is:

A) increasing.
B) decreasing.
C) constant.
D) decreasing and then increasing.