This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuroanatomy, Subject name: Anatomy
Trochlear nerve 
Select and explain. 
A. Supplies the inferior oblique muscle of the eyeball, B. Is the only cranial nerve to emerge from the dorsal aspect of the brainstem, C. Has its nucleus of origin in the midbrain at the level of the superior colliculus, D. Enters the orbit through the middle compartment of the superior orbital fissure
B: Is the only cranial nerve to emerge from the dorsal aspect of the brainstem
Answer: B: Is the only cranial nerve to emerge from the dorsal aspect of the brainstem 
Explanation: (B) Is the only cranial nerve to emerge from the dorsal aspect of the brainstem # TROCHLEAR NERVE emerges from the superior medullary velum near the frenulum veli just below the inferior colliculus.> Trochlear nerve is the only cranial nerve which emerges on the dorsal aspect of the brainstem.> When the trochlear nerve is damaged, diplopia occurs on looking downwards: vision is single so long as the eyes look above the horizontal plane.