The correct option is C Trochlear
The trochlear nerve (the fourth cranial nerve) is a motor nerve, that innervates a single muscle: the superior oblique muscle of the eye which is the muscle of oculomotion (movement of the eyeball). The trochlear nerve is the smallest nerve in terms of the number of axons it contains. It has the greatest intracranial length. Finally, it is the only cranial nerve, that exits from the dorsal aspect of the brainstem.