Information from the left visual field enters the left visual cortex via the a. optic chiasm b. anterior commissure c. superior colliculus d. corpus callosum

I believe the most appropriate answer is a. optic chiasm

From retina, the optic nerve will go to optic chiasm where it will go to the lateral geniculate nucleus and medial colliculus. Medial colliculus will go to the superior colliculus, while lateral geniculate nucleus goes to the visual cortex.
Optic nerve is decussating/crossing at the optic chiasm, not the corpus callosum. Anterior commissure also irrelevant to the visual tract.