A light of wavelength $5890 \text{Å}$ falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light is

• A

  $2.945\times {10}^{-7}\mathrm{m}$

• B

  $3.945\times {10}^{-7}\mathrm{m}$

• C

  $4.95\times {10}^{-7}\mathrm{m}$

• D

  $1.945\times {10}^{-7}\mathrm{m}$