How does pupil diameter change in response to light and what muscles control it?

How does pupil diameter change in response to light and what muscles control it?

• A. They contract in bright light to dilate the pupil; radial muscles contract in dim light to constrict the pupil.
• B. Circular muscles contract in bright light to reduce pupil; radial muscles contract in dim light to dilate the pupil.
• C. Radial muscles contract in bright light to reduce pupil; circular muscles contract in dim light to dilate the pupil.
• D. Both muscle groups contract together to close the pupil.

Answer: (B)