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

Ex Input:
Passage: Figure 32.21 Supernovas are the source of elements heavier than iron. Energy released powers nucleosynthesis. Spectroscopic analysis of the ring of material ejected by Supernova 1987A observable in the southern hemisphere, shows evidence of heavy elements. The study of this supernova also provided indications that neutrinos might have mass. (credit: NASA, ESA, and P. Challis). Answer: supernovas

Ex Output:
What celestial events are the source of elements heavier than iron?

Ex Input:
Passage: An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. For example, the speed of an object down a ramp might be one variable, and the steepness of the ramp might be another. Answer: variable

Ex Output:
In a controlled scientific study, what do you call a factor that can take on different values?

Ex Input:
Passage: Like bacteria, archaeans are important decomposers. For example, archaeans help break down sewage in waste treatment plants. As decomposers, they help recycle carbon and nitrogen. Answer: decomposer

Ex Output:
Archaeans help break down sewage in waste treatment plants, so they fulfill what important role?