This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Reproductive physiology and hormones in females, Subject name: Gynaecology & Obstetrics
[{'content': 'Which among the following is not naturally occurring estrogen? \nSelect and explain. \nA. Estrone, B. Estradiol, C. Estriol, D. Diethylstilbestrol', 'role': 'user'}, {'content': "Answer: D \nExplanation: Estrone, Estradiol and Estriol are natural estrogens The biologically active estrogen is estradiol Estrone and estriol are weaker estrogens Adipose tissue and liver conve androstenedione into estrone Diethylstilbesterol is a synthetic, non-steroidal estrogen of the stilbestrol group. DES is known to cause clear cell carcinoma, a rare vaginal tumor in girls and women who had been exposed to this drug in utero. Ref: Shaw's Textbook of Gynaecology, 15th edition, page no: 309", 'role': 'assistant'}]