Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: If water is so simple, why is it special? Water is one of the few substances that exists on Earth in all three states of matter. Water occurs as a gas, a liquid and a solid. You drink liquid water and use it to shower. You breathe gaseous water vapor in the air. You may go ice skating on a pond covered with solid water ice in the winter. Answer: three matter states
[A]: In how many states does water exist on earth?

[Q]: Passage: Biofuels are useful because they are liquid. Biofuels can go into a gas tank unlike many other types of alternative energy. Answer: liquid
[A]: What form do biofuels take that makes them very useful?

[Q]: Passage: Many common electric devices, such as doorbells, contain electromagnets. If they have moving parts, they are likely to have an electric motor. An electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy. Answer: electromagnets
[A]:
What do electric motors use to change electrical energy into kinetic?