Which activity does economics primarily study

Any point on a country's production possibilities frontier represents a combination of two goods that an economy:

The rybczynski theorem describes: (a) how commodity price changes influence real factor rewards (b) how commodity price changes influence relative factor rewards. (c) how changes in factor endowments cause changes in commodity outputs. (d) how trade leads to factor price equalization.

The role of the credit department includes: a. evaluating customers' credit applications to determine whether they meet the company's approval standards. b. approving all credit applications in order to avoid losing sales. c. collecting cash from customers. d. following unwritten approval standards for processing customers' credit applications.