Stella's marginal utility of the last unit of X consumed is 18 and her marginal utility of the last unit of Y consumed is 12 . What prices for X and Y, respectively, are consistent with Stella being in consumer equilibrium?

A negative externality

a. is an adverse impact on a bystander. b. causes the product in a market to be under-produced. c. is an adverse impact on market participants. d. is present in markets where the good or service does not have any impact on bystanders.

Natural monopolies are usually found in industries with

a. low fixed costs. b. large economies of scale. c. a normal profit. d. constant economies of scale.