You are answering a USMLE-style medical question. Question: An 18-month-old boy is brought to the physician by his mother because of a 2-day history of fever and a pruritic rash that started on his trunk and then progressed to his face and extremities. He has not received any childhood vaccinations because his parents believe that they are dangerous. His temperature is 38.0°C (100.4°F). A photograph of the rash is shown. Which of the following is the most likely diagnosis? Options: A) Nonbullous impetigo B) Varicella C) Rubella D) Erythema infectiosum Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.