page 426 13.1. what is the aggregate demand–aggregate supply model? complete the following passage concerning macroeconomics. one branch of macroeconomics focuses on long-run growth and development, while the other branch focuses on – , which are fluctuations in – , typically over time periods of five years or – . one model that macroeconomists use to study these fluctuations, which are called recessions and expansions, is the – model.