At what point does a consumer stop buying additional units of a product? A. When marginal benefit is more than the marginal cost B. When marginal benefit is more than zero C. When the marginal cost exceeds marginal benefit D. When the marginal cost is equal to the marginal benefit. Help please!

As nina and erin were eating lunch in the central high school student cafeteria, they were discussing the news coverage about the girls' athletic coach being arrested for selling steroids to student athletes. "i think the guy just did it because they don't pay teachers enough money," nina suggested. "i bet the guy had some other kind of drug addiction he was trying to pay for," erin countered. nina and erin's ideas about the cause of the coach's drug-selling behavior are examples of: