Critics of the trichromatic theory of colour vision have indicated that this theory has a major limitation. Which of the following statements MOST accurately reflects this limitation? A) Young and von Helmholtz were incorrect in assuming that cone photoreceptors in our retina are maximally responsive to a specific wavelength of light B) The trichromatic theory cannot explain the phenomenon of visual after-effects C) Rod photoreceptors in our retina, not cones, are responsible for the neural coding of colour D) Research has determined that there are actually six types of cones in the retina, rather than three as proposed by Young and Helmholtz E) Trichromatic theory cannot explain sensory adaptation