Final answer:
The largest cranial nerve is the trigeminal nerve (D). Fifth. It is a mixed nerve responsible for sensory and motor functions of the face and head.
Step-by-step explanation:
Largest Cranial Nerve
The largest cranial nerve is the trigeminal nerve, which corresponds to option (D). Fifth. Humans have 12 cranial nerves, and each has a specific function. The trigeminal nerve, also known as Cranial Nerve V (CNV), is responsible for sensory data such as tactition (pressure), thermoception (temperature), and nociception (pain) from the face and head; it is also responsible for the motor function that allows for biting and chewing. It contains a mix of sensory and motor fibers and is therefore considered a mixed nerve.
The other options mentioned, (A) the olfactory nerve, (B) the facial nerve, and (C) the abducens nerve, serve different functions. The olfactory nerve is primarily a sensory nerve responsible for transmitting the sense of smell, while the facial nerve (Facial, CN VII) contains preganglionic parasympathetic fibers and manages facial expressions and taste from the anterior two-thirds of the tongue. The abducens nerve is primarily a motor nerve controlling eye movement.