Concept:The iris controls the amount of light entering the eye, similar to the diaphragm of a camera.Explanation:The diaphragm in a lens camera adjusts its opening to regulate how much light reaches the film or sensor.In the human eye, the iris performs the same function.The iris expands or contracts to change the size of the pupil.A larger pupil lets in more light, while a smaller pupil lets in less light.This protects the retina and helps form a clear image.Answer:C. Iris