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

Input: Consider Input: Passage: All compounds form when atoms of different elements share or transfer electrons. In water, the atoms share electrons. In some other compounds, called ionic compounds , atoms transfer electrons. The electrons actually move from one atom to another. When atoms transfer electrons in this way, they become charged particles called ions. The ions are held together by ionic bonds. Answer: ions

Output: When electrons move from one atom to another, they become what?

Input: Consider Input: 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

Output: Some species of fish carry their fertilized eggs in their mouth until they hatch; this is called what?

Input: Consider Input: Passage: Generators may produce either alternating or direct current, but they all change kinetic energy to electrical energy. Answer: electrical energy
Output: Generators usually transform kinetic energy into what kind of energy?