In a biprism experiment,monochromatic light of wavelength $\lambda$ is used. The distance between two coherent sources 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
  $\frac{z_{1}}{D_{1}}=\frac{z_{2}}{D_{2}}=\frac{z_{3}}{D_{3}}=\frac{z_{4}}{D_{4}}$
• B
  $z_{1} D_{1}=z_{2} D_{2}=z_{3} D_{3}=z_{4} D_{4}$
• C
  $z_{1} \sqrt{D_{1}}=z_{2} \sqrt{D_{2}}=z_{3} \sqrt{D_{3}}=z_{4} \sqrt{D_{4}}$
• D
  $z_{1} D_{1}^{2}=z_{2} D_{2}^{2}=z_{3} D_{3}^{2}=z_{4} D_{4}^{2}$