The Efficient Output of a Pure Public Good Is Achieved

The efficient output of a pure public good is achieved at the point at which:

A) the marginal benefit obtained by each consumer equals the marginal social cost of producing the good.
B) the sum of the marginal benefits of all consumers equals the marginal social cost of producing the good.
C) the marginal benefit of each consumer equals zero.
D) the marginal social cost of producing the good is zero.
E) both c and d