Final answer:
Sulci, fissures, and gyri are primarily found in the cerebral cortex, which is the highly folded outer layer of gray matter on the cerebrum, maximizing the surface area for neural connections.
Step-by-step explanation:
The sulci, fissures, and gyri are primarily found in the cerebral cortex of the brain. This region, which is the outermost layer of the cerebrum, is made up of a continuous layer of gray matter that is highly folded to maximize the surface area for neuronal connections.
The folding of the cerebral cortex includes the ridges called gyri and the grooves called sulci. Deep sulci are referred to as fissures, with the most prominent being the longitudinal fissure that divides the brain into left and right hemispheres.
While the cerebellum also features gyri and sulci, they are not referred to as such because the structures of the cerebellum are distinctly different and known as folia. Hence the correct answer to where the sulci, fissures, and gyri are primarily found is option C) Cerebral cortex.