In a Young’s double slit experiment, the separation of the two slits is doubled. To keep the same spacing of fringes, the distance D of the screen from the slits should be made 

• A

  $\frac{\mathrm{D}}{2}$

• B

  $\frac{\mathrm{D}}{\sqrt{2}}$

• C

  2D 

• D

  4D