$A$ container is filled with a liquid of refractive index $\mu_1$ up to a depth $d$ and another liquid of refractive index $\mu_2$ up to a depth $d$ is poured on top of it. What is the apparent depth of the container when viewed from above?

• A
  $\left( \frac{d}{\mu_1} + \frac{d}{\mu_2} \right)$
• B
  $\left( \frac{\mu_1 + \mu_2}{d} \right)$
• C
  $\left( \frac{d}{\mu_1} + \frac{d}{\mu_2} \right) \times 2$
• D
  $\left( \frac{\mu_1 \mu_2}{d} \right)$