This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contrast Agents, Subject name: Radiology
[{'content': 'Which of the following is oral contrast agent? \nSelect and explain. \nA. Sonavist, B. Levovist, C. Sono Rx, D. Echogen', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Sono Rx is a oral ultrasound contrast agent Other ultrasound contrast agents Given in the other options are used intravenously', 'role': 'assistant'}]