The opportunity cost of a desired item or outcome to a person is what that person has to give up to get that item or to achieve that outcome. When making decisions, individuals should recognize the opportunity costs of each action that they can take.

Production Possibilities Frontier is a graph that shows the combinations of output that a firm or a society can possibly produce using the available production technology and the given amount of inputs.

A country’s standard of living depends on the economy’s ability to produce goods and services. Since this ability displays great variation across countries, there are huge differences in the living standards of countries around the world.

Efficiency refers to the ability of a firm or society to get the most out of a given level of inputs.

Equity refers to the distribution of resources fairly among members of the society.

As it can be understood from the definitions given the correct answer is “A”.