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

Input: Consider Input: Passage: A metallic bond is the force of attraction between a positive metal ion and the valence electrons that surround itboth its own valence electrons and those of other ions of the same metal. The ions and electrons form a lattice-like structure. Only metals, such as the copper pictured in the Figure below , form metallic bonds. Answer: metallic bond

Output: What is the force of attraction between a positive metal ion and valence electrons?

Input: Consider Input: Passage: Plants alternate between diploid-cell plants and haploid-cell plants. This is called alternation of generations , because the plant type alternates from generation to generation. In alternation of generations, the plant alternates between a sporophyte that has diploid cells and a gametophyte that has haploid cells. Answer: alternation of generation

Output: When plant type alternates from generation to generation what is this called?

Input: Consider Input: Passage: Both flukes and tapeworms are parasites with vertebrate hosts, including human hosts. Flukes live in the host's circulatory system or liver. Tapeworms live in the host's digestive system. Usually, more than one type of host is required to complete the parasite's life cycle. Look at the life cycle of the liver fluke in Figure below . As an adult, the fluke has a vertebrate host. As a larva, it has an invertebrate host. If you follow the life cycle, you can see how each host becomes infected so the fluke can continue its life cycle. Answer: vertebrate
Output: Both flukes and tapeworms are parasites with what kind of host?