You are answering a USMLE-style medical question. Question: An 18-year-old woman comes to the physician because of a pruritic rash on her back for the past 2 hours. This morning, she started a course of ceftriaxone for treatment of pyelonephritis. A photograph of the rash is shown. This patient's skin findings are most likely associated with which of the following? Options: A) Direct tissue damage by irradiated antibiotic agent B) Cytotoxic T-cell destruction of antigen-tagged cells C) Hyperpermeability of superficial dermal microvasculature D) Mast cell activation in subcutaneous tissues Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.