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