In a market system, the primary instruments used to coordinate economic activity are

A firm's marginal cost can always be thought of as the change in total cost if

A) the firm produces one more unit of output. B) the firm buys one more unit of capital. C) the firm's average cost increases by $1. D) the firm moves to the next highest isoquant.

All of the following are true EXCEPT

A) trade between two nations reduces their opportunity costs. B) trade makes nations dependent on each other. C) trade between nations will not benefit all citizens. D) the principle of comparative advantage does not apply to countries with limited resources.