A balance of trade surplus exists when

A) net exports are negative.
B) imports exceed exports.
C) net exports are positive.
D) All of the choices are true.

A balance of trade surplus exists when a country's exports exceed its imports, resulting in a positive net export balance. Therefore, choice C is the correct answer. Choices A and B are incorrect because they describe scenarios where there is a trade deficit, which is the opposite of a trade surplus. Choice D is incorrect because net exports cannot be both positive and negative at the same time.