Final answer:
The cervical plexus is a network of nerves in the neck formed by the ventral rami of the first four cervical nerves and part of the fifth cervical nerve. It includes the phrenic nerve which connects to the diaphragm.
Step-by-step explanation:
The cervical plexus is a network of nerves located deep in the neck. It is formed by the ventral rami of the first four cervical nerves (C1-C4) and part of the fifth cervical nerve (C5). The cervical plexus includes the phrenic nerve, which connects to the diaphragm and plays a key role in respiration.
This means that option D. All of the above are correct is the correct answer.