The iris is a muscle that controls the size of the pupil and therefore, the amount of light that enters the eye.
(The iris; is; a muscle that controls the size of the pupil and therefore) (a muscle; controls; the size of the pupil) (the amount of light; enters; the eye)
The iris a muscle the amount of light
is controls enters
a muscle that controls the size of the pupil and therefore
the size of the pupil
the eye