This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable Diseases, Subject name: Social & Preventive Medicine
[{'content': "Strain used for chickenpox vaccine: \nSelect and explain. \nA. Edmonston Zagreb strain, B. Oka strain, C. 'Danish' 131, D. RA 27/3 strain", 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. b (Oka strain). (Ref. Park PSM 22nd/pg. 137)VACCINESTRAIN USEDMeaslesHDC-Edmonston Zagreb strainBCG'Danish' 131Chicken pox (live attenuated)Oka strainOPVSabin strainIPVSalk strainRubellaRA 27/3 strain", 'role': 'assistant'}]