[单选题]
A beam of unpolarized light .c )kd,eh 2b4x0*m btz)ujlmy in air strikes a flat o1kdl (f1 j7xqdew2d2piece of glass at an angle of dq7(1jo1lf wk edxd22$57.3^{\circ}$. If the reflected beam is completely polarized, what is the index of refraction of the glass?