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: Gynaecology & Obstetrics
[{'content': 'Pelvic outlet is said to be contracted if \nSelect and explain. \nA. Interischial tuberous diameter is < 7 cm, B. Interischial tuberous diameter is < 8 cm, C. Interischial tuberous diameter is < 9 cm, D. Interischial tuberous diameter is < 10 cm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 8cm is threshold to define pelvic outlet contraction.', 'role': 'assistant'}]