Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Magnetic resonance imaging (NMR) devices use liquid nitrogen to cool the superconducting magnets. Nitrogen is a gas at room temperature and liquefies at -195.8°C. Its neighbor on the periodic table (oxygen) boils at -182.95°C. The interactions between nitrogen molecules (N 2 ) are weaker, so the boiling point is lower. Interactions between non-polar molecules depend on the degree of electron fluctuation within the molecule.


Question: Magnetic resonance imaging devices use what to cool the superconducting magnets?
liquid nitrogen
Liquid nitrogen.