(A) Marginal propensity to save -> MPS = 1 - MPC. If 'c' represents MPC, then MPS = 1 - c, matching with (IV).
(B) Marginal propensity to consume -> MPC is the slope of the consumption function C = a + bY, where b represents MPC, matching with (I).
(C) Investment Multiplier -> The multiplier formula is K = 1/MPS, which is the reciprocal of marginal propensity to save, matching with (III).
(D) Average propensity to consume -> APC = C/Y. At the break-even point where consumption equals income (C = Y), APC = Y/Y = 1, matching with (II).
Hence, Option 4: (A) - (IV), (B) - (I), (C) - (III), (D) - (II) -> This matching correctly aligns each macroeconomic concept with its definition. MPS is complementary to MPC (1-c), MPC determines consumption behavior (slope), the multiplier effect is inversely related to savings propensity (1/MPS), and APC equals unity at equilibrium where all income is consumed (break-even point) -> correct