A ray of light moving in air strikes at origin at grazing angle and then follows a path `2y =x^2` for `xge 0`. The correct variation of refractive index with x co-ordinate is:

Options

A. `sqrt(1+4x^2)`
B. `sqrt(1+2x^2)`
C. `sqrt(1+x^2)`
D. `sqrt(1+x^2/2)`