Option 3: (D), (A), (B), (C) -> When people suddenly become more thrifty, the sequential effects are: (D) First, MPS increases and MPC falls as people's behavioral preference shifts toward saving more and consuming less. (A) Second, this decline in MPC leads to a decrease in aggregate consumption spending and aggregate demand. (B) Third, the fall in aggregate demand creates excess supply in the economy, causing firms to reduce production and factor payments, thereby reducing income. (C) Finally, despite the increased propensity to save, there is no change in total savings - this is the 'Paradox of Thrift' where the attempt to save more collectively results in lower income, leaving total savings unchanged at the new equilibrium. This demonstrates how increased thriftiness can be self-defeating at the macroeconomic level. -> correct