Answer:
.c. those that have dealt successfully with the efficiency v. equality trade off and those that haven’t.
Explanation:
Mankiw believed that a country's living standard will be heavily depended on that country's ability to produce economic goods.
Countries that can manage their production efficiently, tend to be able to sold larger amount of products with relatively lower cost. This will lead to more income for the country and the people will have higher living standard because of it,