This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Which pa of the brain is most affected in deep coma ? 
Select and explain. 
A. Brain stem, B. Locus ceruleus, C. Frontal lobe, D. RAS
D: RAS
Answer: D: RAS 
Explanation: Answer- D. RASThe proximity of the RAS to midbrain structures that control pupillary function and eye movements permits clinical localisation of the cause of coma in many cases.preservation of pupillary light reactivity and of eye movements absolves the upper brainstem and indicates that widespread structural lesions or metabolic suppression of the cerebral hemispheres is responsible for coma.