What kind of polarization has a plane electromagnetic wave if the projections of the vector E on

Question:

What kind of polarization has a plane electromagnetic wave if the projections of the vector E on the x and y axes are perpendicular to the propagation direction and are defined by the following equations:
(a) Ex = E cos (wt – kz), Ey = E sin (wt – kz);
(b) Ex = E cos (wt – kz), Ey = E cos (wt – kz + π/4);
(c) Ex = E cos (wt – kz), Ey = E cos (wt – kz + π)?