Answer: The correct answer is "A. Choice (b) describes an externality. The advertising blimp imposes a cost on the motorist that is not accounted for in the market price of advertising. The restriction on coffee exports has market effects, which are not externalities. ".
Explanation: Choice (b) describes an externality. The advertising blimp imposes a cost on the motorist that is not accounted for in the market price of advertising. The restriction on coffee exports has market effects, which are not externalities.
An externality is a situation in which the costs or benefits of producing or consuming a good or service are not reflected in its market price despite having an external impact.
In case A, the situation is reflected in the market price, while in case B, the external situation, despite having an impact, does not affect the market price.