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': "A 10 year old child experiences recurrent skin lesions on her face and upper extremities that rapidly progress to cancer. Xeroderma pigmentosa is considered a possible differential. Which of the following is defective in that case \nSelect and explain. \nA. Topoisomerase, B. 3' → 5' Exonuclease, C. Endonuclease, D. Helicase", 'role': 'user'}, {'content': 'Answer: C \nExplanation: UV rays damage DNA by forming thymidine dimers. This is repaired by the body by nucleotide excision repair. Main enzyme of this mechanism is UV-specific endonuclease.', 'role': 'assistant'}]