This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Effect of ultraviolet radiation on DNA is formation of 
Select and explain. 
A. Purine dimers, B. Pyrimidine dimers, C. DNA-DNA cros linking, D. All of the above
B: Pyrimidine dimers
Answer: B: Pyrimidine dimers 
Explanation: UV light causes the formation of thymine dimers, where covalent bonds are formed between adjacent thymine residuesSince repair mechanism is not operating these mutations are accumulated, leading to cancerRef: DM Vasudevan, 7th edition, page no: 584