Question

superconducting magnets are used in machines called particle accelerators. these machines rely on zero resistance in order to function properly. how are the magnets able to have zero resistance? they are heated to extremely high temperatures. they are cooled to extremely low temperatures. they are made to be very thick. they are made to be very thin.

Explanation:

Superconductivity occurs when materials are cooled to extremely low temperatures, losing all electrical resistance. Heating to high temperatures or changing thickness doesn't cause zero - resistance in the context of superconductivity.

Answer:

They are cooled to extremely low temperatures.