The structures forming the brain stem include
1. the pons
2. the medulla oblongata
3. the midbrain
a 1 and 2 only
b 1 and 3 only
c 2 and 3 only
d 1, 2, and 3

D 1, 2, and 3

Explanation:

Midbrain, pons and medulla oblongata together make the brain stem. The midbrain has the reflex center for the tactile, visual and auditory response while pons serves in the regulation of breathing rate.

Midbrain also contains tracts that pass between cerebrum and cerebellum or spinal cord and serves as a relay station for the same. Medulla oblongata has reflex centers for the heartbeat, breathing, vasoconstriction, sneezing, swallowing, etc.