Concept:The part of the eye that controls light entry by adjusting pupil size is the iris.Explanation:The camera diaphragm is an adjustable opening that controls the amount of light entering the camera.Similarly, the iris controls the amount of light entering the eye by changing the size of the pupil.So the diaphragm is functionally equivalent to the iris, not the cornea, lens, or ciliary muscle.Answer:D. Iris