19. 對於理想變壓器,下列公式何者正確?(A)E1/E2=I1/I2=N1/N2(B)E1/E2=I1/I2=N2/N1(C)E1/E2=I2/I1=N1/N2(D)E2/E1=I1/I2=N1/N2