Suppose the Production of a Good Results in Positive Externalities

Suppose the production of a good results in positive externalities. If output occurs at the intersection of the supply curve and the marginal social benefits curve, then

A) the socially optimal level of output will be produced.
B) society will incur a net social cost.
C) society will want less produced, and producers will be willing to satisfy that desire.
D) there is market failure.