In a double slit experiment the distance between the slits is 0.1 cm and the screen is placed at 50 cm from the slits plane. When one slit is covered with a transparent sheet having thickness t and refractive index n(=1.5), the central fringe shifts by 0.2 cm. The value of t is____ cm

A

$$5.6\times10^{-4}$$

B

$$6.0\times10^{-3}$$

C

$$8\times10^{-4}$$

D

$$5.0\times10^{-3}$$