If $\lambda_0$ and $\lambda$ are the threshold wavelength and the wavelength of incident light,respectively,the velocity of the photoelectron ejected from the metal surface is:

• A
  $\sqrt{\frac{2h}{m}(\lambda_0 - \lambda)}$
• B
  $\sqrt{\frac{2hc}{m}(\lambda_0 - \lambda)}$
• C
  $\sqrt{\frac{2hc}{m} \left(\frac{\lambda_0 - \lambda}{\lambda \lambda_0}\right)}$
• D
  $\sqrt{\frac{2h}{m} \left(\frac{1}{\lambda_0} - \frac{1}{\lambda}\right)}$