20. If a light is propagating with plane electromagnetic waves in vacuum, which of the following statements is incorrect?
(A) The electric and magnetic fields are always perpendicular to the traveling direction.
(B) The electric field is always perpendicular to the magnetic field.
(C) The amplitudes of the electric and magnetic fields can be related with a constant, which is the speed of light.
(D) When the amplitude of electric field reaches its maximum, the amplitude of magnetic field reaches its minimum.