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

[EX 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
[EX A]: In how many states does water exist on earth?

[EX Q]: Passage: Christopher Auyeung, using bat image by User:Rugby471/Wikimedia Commons. Bats use echolocation to identify the location of objects . CC BY-NC 3.0 (bat image available under public domain). Answer: echolocation
[EX A]: What do bats use to determine the location of objects?

[EX Q]: Passage: We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter . Answer: dark matter
[EX A]:
Scientists think that stars and galaxies make up only a small part of the matter in the universe. what is the rest of the matter called?