Final answer:
The large commissure that connects the right and left sides of the brain is the corpus callosum, a thick bundle of nerve fibers essential for interhemispheric communication.
Step-by-step explanation:
The large commissure that connects the right and left sides of the brain is called the corpus callosum. This thick bundle of axons is crucial for allowing communication between the two cerebral hemispheres. By connecting the right and left hemispheres, the corpus callosum facilitates critical interactions like the coordination of motor skills and the sharing of information processed in different lobes, such as the frontal, parietal, temporal, and occipital. The longitudinal fissure is a large separation between the two hemispheres, but it does not connect them; rather, it defines their separation. So the correct answer to the question is C) corpus callosum.