Answer:
b. an infinite set of different wavelength-intensity combinations can elicit the same response from a single type of photoreceptor.
Step-by-step explanation:
The principle of univariance is based on the fact that a visual receptor cell can be excited by different wavelength-intensity combination, so that the brain cannot know the color of a certain point of the retinal image. This means that the same visual receptor cell might not be able to tell the difference between a dim light and a bright or even between lights of different colors.