The Diagram Below Shows the Marginal Cost of Pollution Abatement

The diagram below shows the marginal cost of pollution abatement for two firms,Firm X and Firm Y.
FIGURE 17- 4
-Refer to Figure 17- 4.There is an emissions tax of $t per unit of pollution.Which of the following statements regarding the pollution abatement activities by the two firms is correct?

A) The emissions tax causes no change in the firms' polluting activity.
B) It is efficient for Firm Y to do less pollution abatement than Firm X because Firm Y faces higher costs of abatement.
C) It is not socially optimal to have Firm X doing pollution abatement of QX while Firm Y does the lesser amount,QY.
D) The emissions tax causes an optimal level of pollution.
E) The shaded areas in the two graphs depict the social costs of pollution caused by Firms X and Y.