Final answer:
Cones send combined messages to bipolar cells, while rods may link directly to bipolar cells.
Step-by-step explanation:
The correct answer is d) cones; rod.
In the human eye, cones and rods are the two types of photoreceptor cells found in the retina. Cones are responsible for color vision and function best in bright light, while rods are more sensitive to low light conditions and are responsible for black and white vision. Multiple cones send combined messages to a bipolar cell, whereas a single rod may link directly to a single bipolar cell. This arrangement allows for more precise visual information processing in the cones, while rods provide a more general and sensitive response to light.