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

• Curves a and b represent incident radiations of different frequencies and different intesities

• Curves a and b represent incident radiations of same frequency but of different intesities

• Curves b and c represent incident radiations of different frequencies and different intensities

• Curves b and c represent incident radiations  of same frequency having same intensity