An object that reflects primarily long-wavelength light would most stimulate which category of cone?

The object that reflects primarily long-wavelength light would most stimulate the category of cone that is sensitive to red light. In the human visual system, there are three types of cones that respond to different ranges of wavelengths: short-wavelength cones that respond to blue-violet light, medium-wavelength cones that respond to green light, and long-wavelength cones that are sensitive to red light.

When an object reflects light that possesses longer wavelengths, it will predominantly stimulate the long-wavelength cones. This is why the correct choice relates to the cones responsible for detecting reds. The perception of color is influenced by the specific wavelengths of light that are absorbed and those that are reflected, thus specifically reflecting long-wavelength light will lead to a stronger activation of the red-sensitive cones.