Unpolarized light of intensity I is incident on a system of two polarizers, A followed by B. The intensity of emergent light is I/2. If a third polarizer C is placed between A and B, the intensity of emergent light is reduced to I/3. The angle between the polarizers A and C is θ. Then
a. cosθ=(32)1/4
b. cosθ=(31)1/4
c. cosθ=(31)1/2
d. cosθ=(32)1/2