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

Q: Passage: Energy is absorbed in the process of converting a liquid at its boiling point into a gas. As with the melting of a solid, the temperature of a boiling liquid remains constant and the input of energy goes into changing the state. The molar heat of vaporization of a substance is the heat absorbed by one mole of that substance as it is converted from a liquid to a gas. As a gas condenses to a liquid, heat is released. The molar heat of condensation of a substance is the heat released by one mole of that substance as it is converted from a gas to a liquid. Since vaporization and condensation of a given substance are the exact opposite processes, the numerical value of the molar heat of vaporization is the same as the numerical value of the molar heat of condensation, but opposite in sign. In other words, . Answer: gas

A: Energy is absorbed in the process of converting a liquid at its boiling point into a what?
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Q: Passage: Natural gas is delivered to homes, where it is used for cooking and heating. Natural gas is also a major energy source for powering turbines to make electricity. Natural gas releases most of its energy as heat when it burns. The power plant is able to use this heat, either in the form of hot gases or steam, to spin turbines. The spinning turbines turn generators, and the generators create electricity. Answer: natural gas

A: What type of gas is delivered to homes to use for cooking and heating?
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Q: Passage: 25C is 4.83. Butyric acid is responsible for the foul smell of rancid butter. Answer: butyric acid

A:
What is responsible for the foul smell of rancid butt?
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