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: Physiology
[{'content': 'Estrogen is secreted by ? \nSelect and explain. \nA. Granulosa cells, B. Theca luteal cells, C. Theca interna, D. Theca externa', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Granulosa cells", 'role': 'assistant'}]