The correct answer is B. a study of how tax cuts stimulate aggregate production

This is because the various variables are considered as a unit in the macroeconomic study. In the given case, the demand by various citizens in a nation is studied as a single unit by adding the all over demand is a part of macroeconomic study. On the other hand, the impact of tax cut by the government is impacting the real income of every individual in the economy, which is considered as macroeconomic study.