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
Excessive ultraviolet (uv) radiation is harmful to life. The damage caused to the biological systems by ultraviolet radiation I by: 
Select and explain. 
A. Inhibition of DNA synthesis, B. Formation of thymidine dimmers, C. Ionization, D. DNA fragmentation
B: Formation of thymidine dimmers
Answer: B: Formation of thymidine dimmers 
Explanation: B i.e. Formation of thymidine dimers