instruction:
Given a scientific passage and an answer, generate a question for the given answer.
question:
Passage: Coal is the source of most electricity. Answer: coal
answer:
What is the source of most electricity?

question:
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
answer:
What celestial events are the source of elements heavier than iron?

question:
Passage: A pulley is a simple machine that consists of a rope and grooved wheel. The rope fits into the groove in the wheel, and pulling on the rope turns the wheel. Pulleys are generally used to lift objects, especially heavy objects. The object lifted by a pulley is called the load. The force applied to the pulley is called the effort. Answer: lift
answer:
Pulleys are generally used to do what with objects?