You are answering a USMLE-style medical question. Question: A 71-year-old woman comes to the physician for evaluation of a pigmented lesion on her left foot. She has had decreased appetite and a 6-kg (13-lb) weight loss in the past 2 months. Physical examination shows that on the left medial ankle there is a 2-cm reddish-black nodule with a verrucous surface. A full-thickness excisional biopsy of the lesion shows S100-protein-positive epithelioid cells. A subsequent CT scan of the chest, abdomen, and pelvis shows metastases to the liver; a diagnosis of metastatic melanoma is made. Chemotherapy with aldesleukin is initiated. Which of the following is the mechanism of action for this drug? Options: A) Stimulating release of acute-phase reactants B) Stimulating antigen-processing cells C) Activating natural killer cells and cytotoxic T cells D) Supporting growth of bone marrow stem cells Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.