A ray of light is incident on a surface of glass slab at an angle `45^@`. If the lateral shift produced per unit thickness is `1//sqrt3`, the angle of refraction produced is
A. `tan^-1(sqrt3/2)`
B. `tan^-1(1-sqrt(2/3))`
C. `sin^-1(1-sqrt(2/3))`
D. `tan^-1(sqrt((2)/(3-1)))`