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
All of the following are natural estrogens EXCEPT: 
Select and explain. 
A. Estradiol, B. Ethinylestradiol, C. Estriol, D. Estrone
B: Ethinylestradiol
Answer: B: Ethinylestradiol 
Explanation: Ethinylestradiol is a synthetic steroidal estrogen. All others are natural estrogens. (Ref.Essentials of medical pharmacology 7th edition page no.306)