You are answering a USMLE-style medical question. Question: A 67-year-old man with transitional cell carcinoma of the bladder comes to the physician because of a 2-day history of ringing sensation in his ear. He received this first course of neoadjuvant chemotherapy 1 week ago. Pure tone audiometry shows a sensorineural hearing loss of 45 dB. The expected beneficial effect of the drug that caused this patient's symptoms is most likely due to which of the following actions? Options: A) Inhibition of proteasome B) Hyperstabilization of microtubules C) Generation of free radicals D) Cross-linking of DNA Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.