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': 'The primary defect in Xeroderrna pigmentosa is \nSelect and explain. \nA. Formation of thymidine dimmers, B. Poly ADP ribose polymerase is defective, C. Exonuclease is defective, D. Formation of adenine dimmers.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In xeroderma pigmentos a; nucleotide excision repair of damaged DNA is defective due to formation of TT dimers', 'role': 'assistant'}]