Which of the following is the best explanation of why it is difficult to discriminate the color of an object at night?

A. Cones come in three types, each sensitive to different wavelengths of light.
B. The foveae are densely packed with cones.
C. At night, the amount of light entering the eye is insufficient to stimulate the cone cells but is sufficient to stimulate the rod cells.
D. As many as 100 cones may converge on one ganglion cell.