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 Iso-osmolar agent? \nSelect and explain. \nA. Ionic monomer, B. Ionic dimer, C. Non-ionic monomer, D. Non-ionic dimer', 'role': 'user'}, {'content': 'Answer: D \nExplanation: - Ionic Monomer - High osmolality contrast media - Ionic Dimer - Low osmolality contrast media - Non-ionic Monomer - Low osmolality contrast media - Non-ionic Dimer - Iso osmolality contrast media', 'role': 'assistant'}]