While tariff levels have been falling over the past several decades, nontariff barriers have been used increasingly

Oligopolies are difficult to analyze because

A) oligopolies are a recent development so economists have not had time to develop models. B) demand and cost curves do not exist for these types of industries. C) the firms are so large. D) how firms respond to a price change by a rival is uncertain.

In a two-agent two-good economy, a Pareto-efficient allocation implies that

A) no further mutually beneficial trades are possible. B) agents' indifference curves intersect each other. C) agents' marginal rate of substitution are different. D) agents' marginal rate of transformation are different.