What is the function of ciliary muscles ?

Assists in the accommodation of light from the external environment that penetrates thru our pupil and proceeds in our lens.

Evolutionarily, the eye structure was designed to be at the head specfically superior to the nose, posterior to the skill and distal to the brain and is anteriorly plastered to avoid environmental threats like predators, natural disasters and etc. This way in a functionalist view, the eye has a wider range in getting information from one's environment especially in humans since the eyes in people are the most efficient and powerful sensory organs than the others. In a structural view, the eyes are build in two not only to be able to see one's environment and maximise it but also because the eyes have binocular disparity this means that the eyes will be able to locate an object more cearly and that when one eye is dysfunctional the other can assist the visual imagery of the individual.

Ithink that b is correct but just in case wait to see if someone else answers

The light is great source of energy