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
A 32 week pregnant female presented with labor pain. She was given tocolytics. Which of the following is a tocolytic agent? 
Select and explain. 
A. Prazocin, B. Ritodrine, C. Yohimbine, D. Propranolol
B: Ritodrine
Answer: B: Ritodrine 
Explanation: Betamimetics include ritodrine, terbutaline, albuterol, fenoterol, hexoprenaline, isoxsuprine, metaproterenol, nylidrin, orciprenaline, and salbutamol, they have been used extensively as tocolytic agents. Ritodrine, isoxsuprine and terbutaline are the beta-2 receptor agonists most commonly used. Also know: Other agents used as tocolytic agents are calcium channel blockers, prostaglandin synthase inhibitors, magnesium sulfate, nitric oxide donor and oxytocin receptor antagonists. Ref: Management of High-Risk Pregnancy: A Practical Approach By S. S. Trivedi, Manju Puri, M.D., 2011, Page 81, 82; Danfoh's Obstetrics and Gynecology 10th Edition, Page 175-178.