Contraction of which eye structure controls the amount of light that reaches the retina?
a. Retina
b. Iris
c. Sclera
d. Lens
B
The iris is able to dilate and contract, allowing light to reach the retina. The retina is deep within the eye and does not control the amount of entering light. The sclera is not able to dilate and contract. The lens is merely a transparent disc that acts as a focus for the retina.
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