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

Q: Passage: Sliding friction is friction that acts on objects when they are sliding over a surface. Sliding friction is weaker than static friction. That's why it's easier to slide a piece of furniture over the floor after you start it moving than it is to get it moving in the first place. Sliding friction can be useful. For example, you use sliding friction when you write with a pencil. The pencil "lead" slides easily over the paper, but there's just enough friction between the pencil and paper to leave a mark. Answer: sliding friction

A: What type of friction is friction that acts on objects when they are sliding over a surface?
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Q: Passage: Note Organic and biochemical equations are frequently written showing only the organic reactants and products. In this way, we focus attention on the organic starting material and product, rather than on balancing complicated equations. Ethanol is oxidized in the liver to acetaldehyde:. Answer: products

A: Organic and biochemical equations show the initial and final products of the equation, respectively known as the reactants and what else?
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Q: Passage: The term evolution describes the changes that occur in populations of living organisms over time. Describing these changes does not address the origin of life. The two are commonly and mistakenly confused. Biological evolution likewise says nothing about cosmology, the Big Bang, or where the universe, galaxy, solar system, or Earth came from. Answer: evolution

A:
What process refers to the changes that occur in populations of living organisms over time?
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