13. Xeroderma pigmentosum (XP) is a rare clinical disease associated with sun sensitivity and a high risk for skin malignancy in sun-exposed areas. Which of the following defective DNA repair systems may be involved? (A) Nucleotide excision repair, NER (B) Mismatch excision repair, MMR (C) Base excision repair, BER (D) Non-homologous end joining, NHEJ (E) Double-strand breaks repair, DSBR