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. 
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: UV rays causes DNA damage by forming TT dimers (pyrimidine dimmers) which prevents replication