Given a scientific question, generate a correct answer to it.

Input: Consider Input: The urea cycle, a set of biochemical reactions that produces urea from ammonium ions to prevent toxicity, occurs to some extent in the kidney, but primarily in what organ?

Output: liver

Input: Consider Input: Chewing a bite of bread mixes it with what and facilitates its chemical breakdown?

Output: saliva

Input: Consider Input: Some compounds form rigid frameworks called what?
Output: crystals