Light of wavelength $\lambda$ is incident on a single slit of width $a$ and the distance between the slit and the screen is $D$. In the diffraction pattern, if the slit width is equal to the width of the central maximum, then $D$ is equal to:

• A
  $\frac{a}{\lambda}$
• B
  $\frac{a^2}{\lambda}$
• C
  $\frac{a}{2\lambda}$
• D
  $\frac{a^2}{2\lambda}$