The correct answer is A) How the federal government budget deficit affects interest rates.

As defined in any book of economics, macroeconomics deals with the study of economic issues at aggregate level, aggregate markets, the national government, etc. Microeconomics, on the other hand, focuses on the study of economic issues at individual level, just focusing on the analysis of single markets, the analysis on how firms maximize profits or individuals maximize utility.

B) and D) are not correct since they are focused on phenomena that occur in single markets (this is studied by microeconomics as we just stated) and C) is incorrect since, again, the problems at firm level are studied by microeconomics, not macroeconomics.