Final answer:
The statement that the pupil of the eye is really a circular muscle is true, as the iris, containing the muscle that forms the pupil, adjusts the amount of light entering the eye by contracting and relaxing.
Step-by-step explanation:
The pupil of the eye is really a circular muscle. The answer to this statement is a. True. The iris, which is the colored part of the eye, contains the pupil and is made of smooth muscle that controls the size of the pupil. Circular muscles, also known as sphincters, contract and relax to adjust the size of the opening they surround. Therefore, when it comes to the eye, the iris adjusts the amount of light entering the eye by changing the size of the pupil. When the iris's smooth muscle contracts, the pupil becomes smaller to decrease light entry in bright environments, and when it relaxes, the pupil enlarges to increase light entry in dimmer settings. Furthermore, the extrinsic muscles of the eyes control the movement of the eyeball but do not affect the shape of the pupil directly.