Consider each of the electric- and magnetic-field orientations given next. in each case, what is the direction of propagation of the wave? (a) e in the +x-direction, b in the +y-direction; (b) e in the -y-direction, b in the +x-direction; (c) e in the +z-direction, b in the -x-direction; (d) e in the +y-direction, b in the -z-direction.