Answer: b. they both control the amount of light passing through.
Explanation:
As you may know, the diaphragm of a film camera is used to control the amount of light that passes through and regulates it by changing the size of the hole in front of the camera.
The iris works in a similar way, for example, when you are in a dark room for long enough, your iris will retract and more light will enter in your pupils, while if you are in daylight, your iris will protect your eyes of the intense light. This is the reason that when you are in a dark room and you turn on a light it hurts a little bit, is because your iris are retracted and too much light is passing through.
