In an $X$-ray tube, electrons emitted from a filament (cathode) carrying current $I$ hit a target (anode) at a distance $d$ from the cathode. The target is kept at a potential $V$ higher than the cathode resulting in emission of continuous and characteristic X-rays. If the filament current $I$ is decreased to $\frac{I}{2},$ the potential difference $V$ is increased to $2V,$ and the separation distance $d$ is reduced to $\frac{d}{2},$ then

1. A the cut-off wavelength will reduce to half, and the wavelengths of the characteristic X-rays will remain the same
2. B the cut-off wavelength as well as the wavelengths of the characteristic X-rays will remain the same
3. C the cut-off wavelength will reduce to half, and the intensities of all the X-rays will decrease
4. D the cut-off wavelength will become two times larger, and the intensity of all the X-rays will decrease