In an interference experiment, the spacing between successive maxima or minima is   

• A

  $\frac{\mathrm{\lambda d}}{\mathrm{D}}$

• B

  $\frac{\mathrm{\lambda D}}{\mathrm{d}}$

• C

  $\frac{\mathrm{dD}}{\mathrm{\lambda }}$

• D

  $\frac{\mathrm{\lambda d}}{4\mathrm{D}}$