AS Daily A Level Physics question

In a photoelectric experiment on a clean metal, monochromatic light with frequency 1.5 f0 (f0 is the threshold frequency) produces a stopping potential and a steady photocurrent. At the same time, an electron diffraction tube produces electrons accelerated through a potential V, giving a de Broglie wavelength λ. The light intensity is then doubled, and the accelerating voltage is increased to 4V. Which statement must be true?

1. A The stopping potential is unchanged; the photocurrent doubles; the electron de Broglie wavelength halves. (correct)
2. B The stopping potential doubles; the photocurrent is unchanged; the electron de Broglie wavelength doubles.
3. C No photoelectrons are emitted until the intensity is doubled; the electron de Broglie wavelength is unchanged.
4. D The stopping potential increases by a factor of 4; the photocurrent halves; the electron de Broglie wavelength becomes one quarter of λ.