Statement $(I)$ : By increasing the potential difference between cathode and anode continuously in a photoelectric experiment,the photocurrent always increases continuously.
Statement $(II)$ : If two photons $A$ and $B$ of energies $2.5 \ eV$ and $3.5 \ eV$ respectively fall on a metal surface of work function $2.0 \ eV$,then the ratio of maximum kinetic energies emitted between $A$ and $B$ is $3$.
Statement $(III)$ : The maximum energy needed by an electron to come out from metal surface is called the work function of the metal.
Which of the following is correct?

• A
  Statements $I, II$ and $III$ are true
• B
  Statements $I, II$ are true,but statement $III$ is false
• C
  Statements $II, III$ are true,but statement $I$ is false
• D
  Statements $I, II$ and $III$ are false