In a biprism experiment,monochromatic light of wavelength $\lambda$ is used. The distance between two coherent sources $d$ is kept constant. If the distance between the slit and the eyepiece $D$ is varied as $D_1, D_2, D_3$ and $D_4$,and the corresponding measured fringe widths are $Z_1, Z_2, Z_3$ and $Z_4$,then:

• A
  $Z_1 D_1 = Z_2 D_2 = Z_3 D_3 = Z_4 D_4$
• B
  $\frac{Z_1}{D_1} = \frac{Z_2}{D_2} = \frac{Z_3}{D_3} = \frac{Z_4}{D_4}$
• C
  $D_1 \sqrt{Z_1} = D_2 \sqrt{Z_2} = D_3 \sqrt{Z_3} = D_4 \sqrt{Z_4}$
• D
  $Z_1 \sqrt{D_1} = Z_2 \sqrt{D_2} = Z_3 \sqrt{D_3} = Z_4 \sqrt{D_4}$