[单选题]
A beam of unpolarized light in air strikes a flat piece of glass atkn2v k)mnzs(:ixxv-9 an angleg ma34tqqh+),g eonn8 of q43+ etmn)nq,ha8gog$57.3^{\circ}$. If the reflected beam is completely polarized, what is the index of refraction of the glass?
