In a series of photoelectric emission experiments on a certain metal YA surface, possible relationships between the following quantities were investigated: threshold frequency fo, frequency of incident light f, light intensity P, photocurrent I, maximum kinetic energy Tmax. Two of these quantities, when plotted as a graph of y against x, give a straight line through the origin. Which of the following correctly identifies x and y with the photoelectric quantities? (1996 P1 Q28) 0 O X X y A fo B Tmax C P D P Tmax