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: Pharmacology
[{'content': 'True about atosiban is that it: \nSelect and explain. \nA. Is an oxytocin receptor antagonist, B. Is an progesterone receptor antagonist, C. Is least effective in inhibiting preterm uterine contractions, D. Is a anti–tocolytic drug', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]