The human eye is like a camera that has a lens with :

The human eye is analogous to a camera but with the unique feature of accommodation. The ciliary muscles change the curvature of the eye lens, varying the focal length to focus on objects at different distances. Simultaneously, the iris controls the size of the pupil (aperture) depending on the intensity of incoming light, dilating in dim light and constricting in bright light. Therefore both the focal length and aperture size of the eye lens are variable, making option (d) correct.