Two Firms, a and B, Are Legally Required to Reduce

Two firms, A and B, are legally required to reduce their toxic emissions. If Firm A's marginal cost of abatement is $5 and Firm B's marginal cost of abatement is $5,

A) the socially optimal joint level of abatement is not being achieved.
B) their joint total cost of abatement is at a minimum.
C) Firm B should abate more and Firm A should abate less.
D) their joint total cost of abatement is at a maximum.
E) Firm A should abate more and Firm B should abate less.