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: Biochemistry
[{'content': 'Chemically, oestrogens are characterised by \nSelect and explain. \nA. Absence of O2 at D-17, B. Aromatic character at D-ring, C. Absence to methyl group at C-10, D. A 21-carbon steroid skeleton', 'role': 'user'}, {'content': 'Answer: C \nExplanation: One hydroxyl group attached to the D ring', 'role': 'assistant'}]