Refer to the Figure

Refer to the figure.
If natural gape coloring is dietary, this experiment was most likely to test the prediction that

A) parents preferentially feed offspring with bright red mouths because they are investing in nestlings of high reproductive value.
B) parents preferentially feed offspring with bright red mouths because they use this as signature to recognize the chicks as their own.
C) parents in low quality habitats preferentially feed red-mouthed male offspring because they are more likely to disperse.
D) parents preferentially feed older offspring with more developed red mouths in order to facilitate facultative siblicide.