An electron with velocity V enters the uniform Electric field E and uniform Magnetic field B which are perpendicular to each other. The electron's velocity can stay constant if the velocity is:
a) Perpendicular to E and parallel to B and it has magnitude B/E.
b) Perpendicular to B and it has magnitude E/B.
c) Parallel to E and it has magnitude B/E.
d) Perpendicular to E and B and it has magnitude E/B.