The correct answer is B: Reflection coefficient. The reflection coefficient is the parameter that describes the interaction of a load and transmission line. It quantifies how much of the signal is reflected versus transmitted. The reflection coefficient (Γ, gamma) is the ratio of reflected voltage to incident voltage. It ranges from 0 (no reflection, perfect match) to 1 (total reflection, open or short). The reflection coefficient depends on the load impedance and the transmission line's characteristic impedance. It's related to SWR: SWR = (1+|Γ|)/(1-|Γ|). The reflection coefficient tells you how well the load is matched to the line - a low reflection coefficient means good match, high means poor match. It's a fundamental parameter in transmission line theory.