These paragraphs explain why we can see colors other than green, red, and blue―even though the cones in our eyes are sensitive to just those three colors. Since you have just three types of color detectors in your eyes, it would make sense that the only colors you see would be red, green, and blue. But suppose you're looking at a yellow object. How would your eyes detect a color that isn't an exact match to one of the cones? In this case, the different wavelengths of light for both red and green are reflected into your eyes. The red and green cones send signals of varying strengths to your brain, depending on how excited they are by the different wavelengths. For example, the red cones would be very triggered because more red light is reflected from a yellow object. The green cones would also be triggered, but not as much as the red cones. This triggering of the three different cones to varying degrees is how you see all the different colors. How does this passage of text help readers understand its central idea? A: It defines key terms.
B: It tells a story.
C: It provides an example.
D: It describes a series of steps.