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
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- 
Select and explain. 
A. X-ray of cervical area of neck in flexion and extension, B. MRI brain, C. EMG and NCV within 48 hours, D. Carotid angiography
A: X-ray of cervical area of neck in flexion and extension
Answer: A: X-ray of cervical area of neck in flexion and extension 
Explanation: None