Table 14-12 bill's birdhouses costs revenues quantity produced total cost marginal cost quantity demanded price total revenue marginal revenue 0 $0 -- 0 $80 -- 1 $50 1 $80 2 $102 2 $80 3 $157 3 $80 4 $217 4 $80 5 $285 5 $80 6 $365 6 $80 7 $462 7 $80 8 $582 8 $80 refer to table 14-12. what is the marginal cost of the 5th unit

Which of the following best explains how trade enables greater specialization among producers? a. trade diversifies the market by bringing specialized goods from around the world. b. trade requires distribution networks and adds one more step to the production process. c. trade enables producers to open up new markets for their goods and services. d. trade allows people to focus on one kind of production and trade for their other needs.