The Figure Below Shows the Demand and Supply Curves for Pollution

The figure below shows the demand and supply curves for pollution abatement.
FIGURE 17- 3
-Refer to Figure 17- 3.The MB curve in this diagram is downward sloping because

A) the marginal benefit from a given amount of abatement will be higher,the higher the level of pollution abated.
B) the marginal damage generated by additional units of pollution is decreasing.
C) the marginal cost of additional units of pollution abatement is decreasing.
D) the marginal benefit from a given amount of abatement will be lower,the lower the level of pollution.
E) the marginal cost of additional units of pollution abatement increases as pollution abatement increases.