GATE EC 2001 Electromagnetics Solution Q 1

If a plane electromagnetic wave satisfies the equation  \frac{\partial^2E_x}{\partial z^2}=\frac1{c^2}\frac{\partial^2E_x}{\partial t^2}

the wave propagates in the

(a) x-direction

(b) z-direction

(c) y-direction

(d) xy plane at an angle of 450 between the x and z directions