This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Magnetic Resonance Imaging, Subject name: Radiology
MRI magnet is a 
Select and explain. 
A. Ferromagnet, B. Paramagnet, C. Simple magnet, D. Superconducting-magnet
D: Superconducting-magnet
Answer: D: Superconducting-magnet 
Explanation: MRI uses a Superconducting magnet which is kept cool using Helium. A superconducting MRI magnet comprises a steel cryostat with the superconducting coils immersed in liquid helium at 4.2 Kelvin (-269degC or -452degF).