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

[Q]: Passage: The law of conservation of mass states that matter cannot be created or destroyed. Answer: destroyed
[A]: The law of conservation mass states that matter cannot be created or what?

[Q]: Passage: Mouth Brooding. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding. If you look closely, you can see the eggs inside the mouth of the cardinalfish pictured here. Answer: mouth brooding
[A]: Some species of fish carry their fertilized eggs in their mouth until they hatch; this is called what?

[Q]: Passage: A solution is a mixture of two or more substances that has the same composition throughout. Some solutions are acids, some are bases. Answer: ph
[A]:
Acidity is measured by what physical property?