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: Forensic Medicine
[{'content': 'Most common cause of second trimester aboion: CMC (Vellore) 14 \nSelect and explain. \nA. Chromosomal defect, B. Cervical incompetence, C. Abnormality of uterus, D. Infections', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Cervical incompetence', 'role': 'assistant'}]