For the reaction, 2A + B → products, when the concentrations of A and B both were doubled, the rate of the reaction increased from 0.3 mol L^−1s^−1 to 2.4 mol L^−1s^−1. When the concentration of A alone is doubled, the rate increased from 0.3 mol L^−1s^−1 to 0.6 mol L^−1s^−1. Which one of the following statements is correct ?