The total conductance G_L (solid curves) and the corresponding AR conductance G_A (dotted curves) in lead L through the quadruple QDP chain versus the bias voltage eV. From bottom to top the curves are shifted up by e²/h in turn for clarity, which represent the conductances of the isolated QDP λ_1,2,3,4 = 0, and those of the MBS coupled to QDP 1 (λ_2,3,4 = 0), QDP 2 (λ_1,3,4 = 0), QDP 3 (λ_1,2,4 = 0), and QDP 4 (λ_1,2,3 = 0), respectively. The other parameters are taken to be Γ^L,R = 0.5, t_1,2,3 = 1, v_1,2,3,4 = 1, and ε_M = 0.