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
Which of the following is an oxytocin antagonist ? 
Select and explain. 
A. Ritodrine, B. Atosiban, C. Isoxsuprine, D. Methergine
B: Atosiban
Answer: B: Atosiban 
Explanation: None