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: Biochemistry
[{'content': 'Excessive ultraviolet (uv) radiation is harmful to life. The damage caused to the biological systems by ultraviolet radiation I by: \nSelect and explain. \nA. Inhibition of DNA synthesis, B. Formation of thymidine dimmers, C. Ionization, D. DNA fragmentation', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Formation of thymidine dimers', 'role': 'assistant'}]