Final answer:
Allocative efficiency occurs in an industry when the social benefits match the social costs of production, which in a perfectly competitive market is when Price equals Marginal Cost (P = MC). Option A pertains to allocative efficiency, while option B is incorrect, making the correct answer 'A and B only' with an assumed typo corrected to 'P = MC'. If no typos are assumed, none of the given options fit the definition precisely.
Step-by-step explanation:
When an industry exhibits allocative efficiency, this means that the social benefits of producing a good or service are precisely aligned with the social costs. In a perfectly competitive market, this occurs when P = MC (Price equals Marginal Cost). Therefore, option A—which states that 'every consumer willing to pay at least the marginal cost will get the good'—is a component of allocative efficiency, as it suggests that goods are being distributed to those who value them most, as long as they can cover the cost of production. Option B, on the other hand, is incorrect because ATC (Average Total Cost) does not necessarily equal price in the context of allocative efficiency. Therefore, the correct answer is D, 'A and B only' if we assume a typo in the original question where it should be 'P = MC'. If the options in the question are taken without assuming any typos, then none of the options fully capture the concept of allocative efficiency as defined in economic theory.