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: Orthopaedics
[{'content': 'True about Atlanto-axial joint \nSelect and explain. \nA. Vertebral artery passes posterior to foramen magnum, B. Atlanto-occipital joint has flexion and extension movement, C. Posterior longitudinal ligament does not pass through the spinal canal, D. Atlanto-axial is ellipsoid joint', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]