Which One of the Following Is TRUE

Which one of the following is TRUE?

A) When the social benefits of consuming a good exceed the private benefit enjoyed by the consumer, positive externalities occur.
B) When the social benefits of consuming a good exceed the private benefit enjoyed by the consumer, negative externalities occur.
C) If the private sector fails to provide a public good, the government can correct the market failure by taxing firms that would be capable of providing the good.
D) Perfect competition results in market failure because it leads to an outcome in which the price of the good differs from its marginal cost.