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
Which of the following is oral contrast agent? 
Select and explain. 
A. Sonavist, B. Levovist, C. Sono Rx, D. Echogen
C: Sono Rx
Answer: C: Sono Rx 
Explanation: Sono Rx is a oral ultrasound contrast agent Other ultrasound contrast agents Given in the other options are used intravenously