Final answer:
The corpus callosum connects the left and right hemispheres of the cerebrum, acting as the main communication pathway between them.
Step-by-step explanation:
The structure that connects the left and right hemispheres of the cerebrum is the corpus callosum. This thick bundle of axons lies deep within the brain and is the principal method for communication between the two cerebral hemispheres. The other options provided, such as the choroid plexus, longitudinal fissure, and central sulcus, serve different functions in the brain. The choroid plexus is involved in the production of cerebrospinal fluid; the longitudinal fissure is the deep groove that separates the two hemispheres; and the central sulcus is a fold in the cerebral cortex that separates the frontal and parietal lobes.