According to the opponent-process theory,cells that are turned "on" by

A) green light are turned "off " by blue light.
B) yellow light are turned "off " by red light.
C) green light are turned "off " by red light.
D) red light are turned "off " by blue light.

According to the opponent-process theory, cells responsible for detecting green light are also sensitive to red light, and they are inhibited or turned "off" by it. Similarly, cells responsible for detecting red light are inhibited by green light. This can explain phenomena like the afterimage effect, where staring at a green image for a while can make a subsequent red image appear even more intense. Yellow and blue are not directly involved in this process, so choices A and D are incorrect.