The figure shows a plot of photo current versus anode potential for a photo sensitive surface for three different radiations. Which one of the following is a correct statement?

• A
  Curves $(b)$ and $(c)$ represent incident radiations of same frequencies having same intensity.
• B
  Curves $(a)$ and $(b)$ represent incident radiations of same frequencies but of different intensities.
• C
  Curves $(a)$ and $(b)$ represent incident radiations of different frequencies and different intensities.
• D
  Curves $(b)$ and $(c)$ represent incident radiations of different frequencies and different intensities.