Answer:
The answer is: A) the study of how prices are determined in the baseball card industry
Step-by-step explanation:
Microeconomics is concerned with single factors (individuals or an specific company or industry) and the effects of their decisions and allocation of resources. The baseball card industry and their pricing methods enter into this category.
While the country´s unemployment rate, or the Fed´s interest rate, or national politics affect the whole economy, so they part of Macroeconomics.