An observer moves towards a stationary source of sound with a speed 1/5th of the speed of sound.  The wavelength and frequency of the source emitted are $\mathrm{\lambda } \mathrm{and} \mathrm{f}$ , respectively.  The apparent frequency and wavelength recorded by the observer are respectively.

• A

  $\mathrm{f},1.2\mathrm{\lambda }$

• B

  $0.8\mathrm{f},0.8\mathrm{\lambda }$

• C

  $1.2\mathrm{f},0.83\mathrm{\lambda }$

• D

  $1.2\mathrm{f},\mathrm{\lambda }$