The Coase theorem states that,in the presence of externalities,a market economy will:

A) always reach an efficient solution.
B) never reach an efficient solution.
C) reach an efficient solution if transaction costs are sufficiently low and property rights are well-defined.
D) reach an efficient solution only in the case of government regulation.

The Coase theorem states that in the presence of externalities, a market economy can reach an efficient solution through bargaining and negotiation between affected parties, as long as transaction costs are sufficiently low and property rights are well-defined. Therefore, choice C is the correct answer. Option A is incorrect because the Coase theorem does not guarantee that an efficient solution will always be reached. Option B is incorrect because the Coase theorem does offer a potential solution for externalities. Option D is incorrect as it suggests that only government intervention can result in an efficient solution, but the Coase theorem suggests that voluntary agreements between parties can also be effective.