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

Input: Consider Input: Passage: Some nonmetals are very reactive, whereas others are not reactive at all. It depends on the number of electrons in their outer energy level. Answer: reactivity

Output: The number of electrons in the outer energy level determines what property of nonmetals?


Input: Consider Input: Passage: boundary between air masses that is stalled in one place. Answer: aids

Output: Opportunistic diseases are usually the direct cause of death of people with what disease?


Input: Consider Input: Passage: Scientists compare the anatomy, embryos, and DNA of living things to understand how they evolved. Evidence for evolution is provided by homologous structures. These are structures shared by related organisms that were inherited from a common ancestor. Other evidence is provided by analogous structures. These are structures that unrelated organisms share because they evolved to do the same job. Answer: analogous structures


Output: What type of structures evolved to do the same job by unrelated organisms?


