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
[{'content': 'Subacute Combined Degeneration of Cord due to deficiency of? \nSelect and explain. \nA. Vitamin B1, B. Vitamin B5, C. Vitamin B6, D. Vitamin B12', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Answer is D (Vitamin B12): Subacute Combined Degeneration of Cord (SACD) is caused by vitamin B,2 deficiency. Subacute Combined Degeneration Of Cord is a condition of the spinal cord characterized by demyelination of its neurons due to deficiency of Vit B12,which results in defective/ deficient myelination. Such demyelination occurs predominantly in Posterior column of spinal cord Pyramidal tract of spinal cord Subacute Combined Degeneration of Cord Degeneration/Demyelination of Posterior column of lower cervical & upper thoracic region This is where changes commence. Paraesthaesias, consisting of tingling & numbness and that of pins & needlesQ Loss of vibration sense Q Position sense is involved to a lesser extent. Q Ataxic gait Q Degeneration/Demyelination of Lateral columns (coicospinal tracts) Their involvement follows the involvement of post columns. Motor defecits such as weakness and spasticityQ Increased deep tendon reflexes, clonusQ Plantar extensor Q Spastic gait (Note that gait is initially ataxic but later becomes both spastic and ataxic. Q (at an early stage patellar & achilles reflexes may be diminished, increased or absent).', 'role': 'assistant'}]