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

[EX Q]: Passage: Figure 24.13 The lifecycle of an ascomycete is characterized by the production of asci during the sexual phase. The haploid phase is the predominant phase of the life cycle. Answer: asci
[EX A]: The lifecycle of an ascomycete is characterized by the production of what during the sexual phase?

[EX Q]: Passage: The rock of the mantle is mostly peridotite. Peridotite is formed of crystals of olivine (green) and pyroxene (black). Answer: peridotite
[EX A]: The rock of the mantle is mostly what?

[EX Q]: Passage: Air pollution may also cause acid rain. This is rain that is more acidic (has a lower pH) than normal rain. Acids form in the atmosphere when nitrogen and sulfur oxides mix with water in air. Nitrogen and sulfur oxides come mainly from motor vehicle exhaust and coal burning. Answer: air pollution
[EX A]:
Acid rain may be caused by what?