You are answering a USMLE-style medical question. Question: A 20-year-old male college student presents to the emergency room at 4 AM in the morning with complaints of abdominal cramps, nausea, vomiting, and diarrhea for the past 2 hours. He was studying for his exams last night when he became hungry and ate some food from the afternoon after heating it for a while. He says that his symptoms began an hour after he ate the food. His temperature is 37°C (98.6°F), respiratory rate is 15/min, pulse is 106/min, and blood pressure is 90/78 mm Hg. A physical examination is within normal limits except for signs of dehydration. What is the most likely diagnosis? Options: A) Cryptosporidiosis B) C. difficile colitis C) Bacillus cereus infection D) Norovirus infection Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.