Concept:The pupil is the circular opening in the centre of the iris that allows light to enter the eye and reach the retina.
Explanation:Light first passes through the cornea, the transparent front layer of the eye.
It then enters through the pupil, which is the actual opening in the eye.
The size of the pupil is controlled by the iris muscles, which adjust the amount of light entering.
However, the pupil itself is the opening through which light travels to the lens and then to the retina.
The cornea is only a protective cover, not an opening.
The iris is the coloured muscular part that surrounds the pupil.
The optic nerve transmits visual signals from the retina to the brain, so it is not the opening.
Answer:A. pupil