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

Answer: In a chemical reaction, what, in general, comes together in order to form a product?

Question: Passage: Centrioles are rod-like structures made of short microtubules. Nine groups of three microtubules make up each centriole. Two perpendicular centrioles make up the centrosome . Centrioles are very important in cellular division, where they arrange the mitotic spindles that pull the chromosome apart during mitosis. Answer: centrioles

Answer: What are the rod-like structures made of short microtubules that play an important part in cellular division?

Question: Passage: Conservation of charge is the fourth of the five conservation laws in physics. There are two charges, positive and negative, and the conservation of electric charge indicates that the total charge in the universe remains the same. In any closed system charge can be transferred from one body to another or can move within the system but the total electric charge remains constant. Answer: positive and negative

Answer:
What are the two types of charges?