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

Example Input: What states that chemical reactions occur when atoms, ions, or molecules collide?
Example Output: collision theory

Example Input: Like all tetrapods except birds and mammals, frogs possess a heart with what structure?
Example Output: three chambers

Example Input: Arguably the most important ingredient in saliva for digestion is a type of what, which initiates the breakdown of carbohydrates?
Example Output:
enzyme