In two setups of Young’s double – slit experiment, if lights used have the ratio of wavelengths as 1 : 2, then fringes of equal width are observed. If the ratio of slit separation is 2 : 1 then the ratio of the distance between slit and screen $D_1 : D_2$ will be

• A

  1 : 1

• B

  1 : 4

• C

  2 : 1

• D

  4 : 1