$A$ cubic block of glass with refractive index $n_1$ is in contact with the surface of water with refractive index $n_2$. $A$ ray of light is incident on the vertical face of the block (see figure). After refraction,total internal reflection at the base,and refraction at the opposite vertical face,the ray emerges at an angle $\theta$. The value of $\theta$ is given by:

• A
  $\sin\, \theta < \sqrt {{n_1}^2 - {n_2}^2} $
• B
  $\tan\, \theta < \sqrt {{n_1}^2 - {n_2}^2} $
• C
  $\sin\, \theta < \frac{1}{{\sqrt {{n_1}^2 - {n_2}^2} }}$
• D
  $\tan\, \theta < \frac{1}{{\sqrt {{n_1}^2 - {n_2}^2} }}$