This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Which of the following contrast agent is non iodinated: 
Select and explain. 
A. lohexol, B. Diatrizoate, C. Gadolinium, D. Visipaque
C: Gadolinium
Answer: C: Gadolinium 
Explanation: C i.e. Gadolinium