This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Anatomy
[{'content': 'CPD in absence of gross pelvic abnormality can be diagnosed by \nSelect and explain. \nA. Ht of mother < 158 cms, B. Trial of labor, C. X ray pelvimetry, D. Pelvic examination', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Best method to rule out CPD is trial of labor Best investigation MRI', 'role': 'assistant'}]