A beam of unpolarised light is passed first through tourmaline crystan A and then through another tourmaline crystal B oriented so that its principal plane is parallel to that of A. The intensity of the emergent light is I. If A now rotated by `45^(@)` in a plane perpendicular to the direction of the incident ray, the intensity of the emergent light will be
A. `I/2`
B. `I/sqrt(2)`
C. `I`
D. `I/4`