The Efficient Output of a Public Good Occurs at the Point

The efficient output of a public good occurs at the point where the:

A) curve formed by the horizontal summation of marginal benefit curves of users intersects the marginal cost curve.
B) curve formed by the horizontal summation of the individual demand curves intersects the marginal cost curve.
C) curve formed by the vertical summation of all users' demand curves intersects the marginal cost curve.
D) curve formed by the vertical summation of the social cost curves intersects the social benefit curve.