The aim of the study of macroeconomics is to examine the interactions between individual producers and consumers. the economy's behavior. the relationship between supply and demand. the economy's viability.

"macro" means "whole" or "big-scale" - so macroecomomics means Economics on a big scale, examining the properties of economy as a whole, as opposed to examining only parts of the economy.

The best answer is then: the economy's behaviour (that is, the behaviour of the economy as a whole).