A person is obliged to choose between buying a sewing-machine and a radio. He buys the radio. The opportunity cost of the radio may be said to be

The correct answer is: B. the sewing-machine he had to do without.

Opportunity cost is the cost of something in terms of the next best alternative that is forgone. In this case, the person had to choose between buying a sewing-machine and a radio. He chose to buy the radio, so the opportunity cost of the radio is the sewing-machine he had to do without.

A is incorrect because the satisfaction obtained from the purchase of the radio is not the same as the opportunity cost. The opportunity cost is what the person had to give up in order to get the radio, not how much satisfaction they got from it.

C is incorrect because the scarcity value of the radio in money terms is not the same as the opportunity cost. The opportunity cost is what the person had to give up in order to get the radio, not how much money it is worth.

D is incorrect because the average cost of both commodities is not the same as the opportunity cost. The opportunity cost is what the person had to give up in order to get the radio, not the average cost of both commodities.