At what point does the optimal level of pollution abatement in the steel industry occur? a. where the marginal private cost of abatement is equal to the marginal social benefit from abatement O b. where the total cost of abatement is equal to the total benefit from abatement O c. where the marginal social cost of producing steel is equal to the demand for steel O d. where the marginal social cost of abatement is equal to the marginal social benefit from abatement