A proton moving with a constant velocity passes through a region of space without any change in its velocity. If E and B represent the electric and magnetic field intensities respectively, then this region of space may not have

• A

  $E=0 ; B=0$

• B

  $E=0,B\ne 0$

• C

  $E\ne 0,B=0$

• D

  $E\ne 0,B\ne 0$