The Great Depression of the 1930s and the Great Recession, which began in 2007, stand out with distinctions among all other recessions observed in the last 100 years. (a) What unique macroeconomic lesson do they teach us? (b) Use the IS-LM-AD model augmented by inflation expectations to explain the above lesson. In particular, state and explain the underlying macroeconomic fundamentals responsible for a prolonged contraction in national income with rising unemployment. Use suitable diagrams to support your answer.