Option 4: (A) - (IV), (B) - (III), (C) - (I), (D) - (II) -> Let's understand each matching: (A) Marginal Rate of Substitution (MRS) is the slope of the indifference curve, representing the rate at which a consumer is willing to substitute one good for another while maintaining the same level of satisfaction, hence matches with (IV). (B) MUₓ/MUᵧ=Pₓ/Pᵧ is the consumer equilibrium condition expressing the law of equi-marginal utility, which states that at optimal consumption, the ratio of marginal utilities equals the ratio of prices, hence matches with (III). (C) -(Pₓ/Pᵧ) represents the slope of the budget line, showing the rate at which the market allows substitution between goods based on their prices, hence matches with (I). (D) Monotonic Preferences means consumers always prefer more of at least one good and no less of the other good (the 'more is better' principle), hence matches with (II). -> correct