How many different types of cones make up normal human color vision?

A) two
B) three
C) four
D) five

Normal human color vision is trichromatic, meaning it is based on the presence of three types of cones in the retina that detect different frequencies of light. These cones are often referred to as "red," "green," and "blue" cones, although they are actually most sensitive to longer, medium, and shorter wavelengths of light, respectively.