Which two parts make up the brain's structure when examined from the top?

The cerebral hemispheres are the correct answer because they are the two large halves of the brain that are visible when viewed from above. These hemispheres are responsible for a variety of functions including cognition, sensory processing, and motor control. The left and right hemispheres communicate with each other through a structure called the corpus callosum, and each hemisphere is associated with different functions, such as language and spatial reasoning.

The other options do not represent the top structure of the brain effectively. For instance, the cerebellum is located under the cerebral hemispheres and is primarily involved in coordination and balance, while the cortex refers to the outer layer of the cerebral hemispheres but does not stand alone as a distinct part when referencing the structure from above. The frontal and occipital lobes are specific regions within the cerebral hemispheres, thus not representing the top structure in its entirety. Finally, the brainstem and spinal cord are located beneath the cerebral hemispheres and are not visible from a top-down view. This reinforces why the cerebral hemispheres are the focal point when discussing the brain's structure from a bird's-eye perspective.