In a Fraunhofer diffraction,light of wavelength $\lambda$ is incident on a slit of width $d$. The diffraction pattern is observed on a screen placed at a distance $D$. If the linear width of the central maximum is equal to two times the width of the slit,then the value of $D$ is:

• A
  $\frac{d^2}{\lambda}$
• B
  $\frac{d^2}{2 \lambda}$
• C
  $\frac{d^2}{3 \lambda}$
• D
  $\frac{d^2}{4 \lambda}$