Answer
(a) green
(b) red
(c) blue
Work Step by Step
(a) We know that the color of the curve corresponding to an incident beam that is unpolarized is green. The unpolarized light is reduced in intensity by a factor of 2 regardless of the angle of the transmission axis.
(b) We know that the color of the curve corresponding to an incident beam that is vertically polarized is red. At $\theta=0$, we have complete transmission that is vertically polarized.
(c) The color of the curve corresponding to an incident beam that is horizontally polarized is blue. At $\theta=0$, there is no transmission which means the incident light is horizontally polarized.
