The brainstem comprises of:

a. midbrain

b. medulla

c. pons

d. all of the above

e. a and c only

All of the above.

Explanation:

The brain stem is present in the posterior part of the brain. This stem is continuous with the spinal cord. The sensory and motor nerve supply are originated from the brainstem.

The brain stem include the medulla, pons and the midbrain. The cardiac and respiratory function of the body is regulated by the brainstem. The sleep cycle of the body is also regulated by the brainstem.

Thus, the correct answer is option (d).