You are answering a USMLE-style medical question. Question: A 14-year-old girl is brought to the physician by her father because of fever, chills, abdominal pain, and profuse non-bloody diarrhea. Her symptoms began one week ago, when she had several days of low-grade fever and constipation. She returned from Indonesia 2 weeks ago, where she spent the summer with her grandparents. Her temperature is 39.3°C (102.8°F). Examination shows diffuse abdominal tenderness and mild hepatosplenomegaly. There is a faint salmon-colored maculopapular rash on her trunk and abdomen. Which of the following is the most likely causal organism? Options: A) Giardia lamblia B) Schistosoma mansoni C) Salmonella typhi D) Clostridium perfringens Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.