Final answer:
The theory that emphasizes the idea that color vision depends on the relative responses of three kinds of cones is A. Trichromatic theory
Step-by-step explanation:
The trichromatic theory, also known as the three-primary-color theory. According to this theory, there are three types of cones in our eyes that are each responsive to a different wavelength: short (S) cones for blue light, medium (M) cones for green light, and long (L) cones for red light. By combining the responses of these three types of cones, we are able to perceive a wide variety of colors.
For example, if an object reflects primarily green light, the M cones in our eyes will be most strongly activated, and we will perceive the object as green.
In contrast, the opponent-process theory (answer choice B) suggests that color vision is based on pairs of opposing colors (black-white, yellow-blue, and green-red). However, this theory is more relevant to the processing of color signals in the visual system after they leave the retina and travel to the brain. Therefore the correct answer is A. Trichromatic theory