This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Brain , Subject name: Anatomy
All of the following form the floor of third ventricle, except 
Select and explain. 
A. Infundibulum, B. Occulomotor nerve, C. Mammillary body, D. Optic chiasma
B: Occulomotor nerve
Answer: B: Occulomotor nerve 
Explanation: Floor of third ventricle is formed from before backward by :Optic chiasmaTuber cinerum & infundibulumMammillary bodiesPosterior perforated substanceTegmentum of midbrain(Ref: Vishram Singh textbook of clinical neuroanatomy second edition pg 137)