You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Bonds break and reform during chemical reactions. Reactants and products contain the same atoms, but they are rearranged during the reaction, so reactants and products are different substances. Answer: reactants
Output:
In a chemical reaction, what, in general, comes together in order to form a product?