The figure shows the variation of photocurrent with anode potential for a photosensitve surface for three different radiations. Let `l_a, l_b and l_c` be the curves a, b and c, respectively
(a) `f_a = f_b and l_a != l_b` (b) `f_a = f_c and l_a = l_c`
(c ) `f_a = f_b and l_a = l_b` (d) `f_b = f_c and l_b = l_c`