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: Gynaecology & Obstetrics
[{'content': 'Naturally occuring estrogens are:a) Estroneb) Estrad iolc) Estriold) Diethylstilbesterole) Pregnanediol \nSelect and explain. \nA. ab, B. bc, C. abc, D. bcd', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Natural estrogens are C18 steroids\nMain Source - Theca and granulosa cells of Graafian follicle and corpus luteum.\nSecondary source - Adrenal cortex\n\n\nNaturally occurring estrogen\n\n\nEstradioI – Main estrogen during reproductive years,\nEstrone (Produced by peripheral aromatization of androstenedione) - Main estrogen after menopause\nEstriol (the main source is placenta) - Main estrogen during pregnancy. It is a marker of feto-maternal-placental well being.', 'role': 'assistant'}]