Do you think the way Zea mays responded to light (or didn’t respond to light) benefits the plant? How might the ability to change phenotype or genotype generally benefits plants?

yes, because even though a theory has a  lot of evidence to support it, it is not always true

i believe it's c. the trait for large beaks will be passed on to future generations through natural selection.

since eventually smaller beaks would have to find another source of food or even eventually just die out from the lack of food.