This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
[{'content': 'True about tamoxifen is- \nSelect and explain. \nA. Selective estrogen receptor downregulator, B. Selective estrogen receptor modulator, C. Selective tissue estrogen activator regulator, D. Estrogen antagonist', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., SERM * Has been explained in previous sessions", 'role': 'assistant'}]