a)to a lower intensity.
b)toward longer wavelengths.
c)toward higher energies.
d)to a higher intensity.
Light emitted by an object moving toward you shifts into higher frequencies, and light emitted by something moving away from you shifts into lower frequencies. If you understand the relationship between energy, frequency, and wavelength, then this should enable you to answer this question.
An object moving towards us has its spectrum shifted towards the blue end (higher frequencies).