You are answering a USMLE-style medical question. Question: A 29-year-old woman comes to the physician with high-grade fever, headache, and muscle pain. A week ago, she returned from India, where she was working with an NGO to build houses in rural areas. The patient took one dose of chloroquine one week before her trip. She also took a further dose during her trip. She has no history of a serious illness. Her temperature is 39.3°C (102.7°F), pulse is 102/min, respirations are 22/min, and blood pressure is 112/78 mm Hg. Physical examination shows jaundice. The abdomen is soft and nontender. The remainder of the examination shows no abnormalities. Her hemoglobin concentration is 10 g/dL and a blood smear shows fragmented erythrocytes and occasional ring-shaped inclusion bodies within erythrocytes. Which of the following is the most likely cause of infection in this patient? Options: A) Plasmodium ovale B) Plasmodium falciparum C) Chikungunya virus D) Hepatitis A virus Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.