Light of frequency $f$ is incident on a metal surface. The work function of the metal is $\phi$. Which of the following is the maximum kinetic energy of the electrons emitted from the surface?

A.     $hf - \phi$

B.     $\frac{h}{e}(f - \phi )$

C.     $\phi  - hf$

D.     $\frac{h}{e}(\phi  - f)$

A