$A$ double slit experiment is immersed in water of refractive index $n = 1.33$. The slit separation is $d = 1 \text{ mm}$, and the distance between the slit and the screen is $D = 1.33 \text{ m}$. The slits are illuminated by light of wavelength $\lambda_0 = 6300 \text{ Å}$ in vacuum. The fringe width is:

• A
  $4.9 \times 10^{-4} \text{ m}$
• B
  $6.3 \times 10^{-4} \text{ m}$
• C
  $8.6 \times 10^{-4} \text{ m}$
• D
  $5.8 \times 10^{-4} \text{ m}$