question: Q:An 84-year-old man comes to the emergency department because of lower back pain and lower extremity weakness for 3 weeks. Over the past week, he has also found it increasingly difficult to urinate. He has a history of prostate cancer, for which he underwent radical prostatectomy 8 years ago. His prostate-specific antigen (PSA) level was undetectable until a routine follow-up visit last year, when it began to increase from 0.8 ng/mL to its present value of 64.3 ng/mL (N < 4). An MRI of the spine shows infiltrative vertebral lesions with a collapse of the L5 vertebral body, resulting in cord compression at L4–L5. The patient receives one dose of intravenous dexamethasone and subsequently undergoes external beam radiation. Which of the following cellular changes is most likely to occur as a result of this treatment?? 
  {'A': 'Formation of pyrimidine dimers', 'B': 'Disruption of microtubule assembly', 'C': 'Intercalation of neighbouring DNA base pairs', 'D': 'Generation of hydroxyl radicals', 'E': 'Formation of DNA crosslinks'},