The brainstem is the posterior part of the brain that connects the cerebrum and cerebellum with the spinal cord. It consists of three major parts :

1. Midbrain (Mesencephalon) : The most superior portion of the brainstem. It contains the cerebral peduncles, which are nerve tracts that connect the cerebrum to the pons and medulla. The midbrain is involved in functions such as vision, hearing, eye movement, and body movement.
2. Pons : The middle portion of the brainstem located between the midbrain and the medulla oblongata. It is involved in the regulation of breathing, communication between different parts of the brain, and sensations such as hearing, taste, and balance.
3. Medulla Oblongata : The most inferior portion of the brainstem. It is continuous with the spinal cord at the foramen magnum of the skull. The medulla oblongata controls autonomic functions such as breathing, heart rate, and blood pressure.

Therefore, the correct answer is Option A : Mid-brain, Pons, and Medulla Oblongata.