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

Q: Passage: An ideal engine, the most efficient theoretically possible, is called a Carnot Engine. Its efficiency is given by the following formula, where the temperatures are, respectively, the temperature of the exhaust environment and the temperature of the heat input, in Kelvins. In a Carnot engine heat is input and exhausted in isothermal cycles, and the efficiency is . In all real engines heat is lost to the environment, thus the ideal efficiency is never even close to being obtained. Answer: carnot engine

A: What is the name of the the most efficient possible engine?
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Q: Passage: Carbon doesn't stop there. Living things get energy from food in a process called respiration. This releases carbon dioxide back into the atmosphere. The cycle then repeats. Answer: carbon dioxide

A: Living things get energy from food in a process called respiration, which releases what gas back into the atmosphere?
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Q: Passage: Biochemical compounds are carbon-based compounds that make up living organisms. There are four main classes of biochemical compounds: carbohydrates, proteins, lipids, and nucleic acids. The classes have different structures and functions. Answer: biochemical

A:
Living organisms are made up of what type of carbon-based compounds?
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