Final answer:
The pons is the structure that connects the brain and the spinal cord, forming an essential part of the brainstem. So, the correct answer is option d.
Step-by-step explanation:
The structure that connects the brain and the spinal cord is the brainstem, which consists of the midbrain, medulla oblongata, and the pons. Therefore, the correct answer to the question is D. pons. The pons serves as the main connection between the cerebellum and the rest of the brain, as well as being an integral part of the brainstem that facilitates crucial functions such as cardiovascular and respiratory system regulation. It acts as a bridge conveying messages between the brain and the body, and also relays sensory and motor signals to and from the spinal cord.
So, the correct answer is option d.