A production function Q = f(K,

Euler's Theorem states: nQ = (∂Q/∂K)·K + (∂Q/∂L)·L. Under CRS (n = 1): Q = MP₂ₖ·K + MPₗ·L. In competitive markets, factors earn their marginal products (r = ∂Q/∂K, w = ∂Q/∂L), so Q = r·K + w·L — total output exactly exhausts total factor payments. This is the Product Exhaustion Theorem. Why others are wrong: • (B) — Marginal products must be multiplied by factor quantities, not simply summed. • (C) — Doubling only K with L fixed does NOT double output under CRS; both inputs must scale proportionally. • (D) — n = sum of output elasticities holds for any homogeneous function, not exclusively Cobb-Douglas.