An ionized gas contains both positive and negative ions. If it is subjected simultaneously to an electric field along the +x-direction and a magnetic field along the +z-direction, then [2000S]
a. positive ions deflect towards +y-direction and negative ions towards −y direction
b. all ions deflect towards +y-direction
c. all ions deflect towards −y-direction
d. positive ions deflect towards −y-direction and negative ions towards +y-direction.