The following diagram shows society's marginal benefit and marginal cost for abating a particular type of pollutionsay

Question:

The following diagram shows society's marginal benefit and marginal cost for abating a particular type of pollution€”say greenhouse-gas emissions.

a. Explain why the marginal cost curve is upward sloping.
b. Explain why the marginal benefit curve is downward sloping.
c. At Q*, are all greenhouse-gas emissions eliminated? Explain.
d. Is there an "optimal" level of greenhouse-gas emissions? Explain.