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': 'A patient of rheumatoid arthritis presents with progressive quadri-paresis and weakness, Babinsky sign was positive, increased muscle tone of limbs with exaggerated tendon jerks and worsening of gait with no sensory, sphincter involvement. Best initial investigation is- \nSelect and explain. \nA. X-ray of cervical area of neck in flexion and extension, B. MRI brain, C. EMG and NCV within 48 hours, D. Carotid angiography', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]