Scattered Light in the Atmosphere Is Often Partially Polarised

Multiple Choice

Scattered light in the atmosphere is often partially polarised.The best way to determine whether or not light from a particular direction in the sky shows polarisation is to:

A) diffract the light through a single slit.
B) squint while looking in that direction.
C) rotate a piece of polaroid film about an axis parallel to the ray while looking through it in that sky direction.
D) rotate a piece of polaroid film about an axis perpendicular to the ray while looking through it in that sky direction.
E) reflect the rays from that direction on a shiny metal surface.