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

[EX Q]: Passage: Steel is an example of an alloy. An alloy is a mixture of a metal with one or more other elements. The other elements may be metals, nonmetals, or both. An alloy is a solid solution. It is formed by melting a metal and dissolving the other elements in it. The molten solution is then allowed to cool and harden. Several other examples of alloys and their uses are shown in Figure below . You can learn about an amazing alloy called memory wire at the URL below. If you have braces on your teeth, you may even have this alloy in your mouth!. Answer: an alloy
[EX A]: A mixture of a metal with one or more other elements is called?

[EX 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
[EX A]: What type of friction is friction that acts on objects when they are sliding over a surface?

[EX Q]: Passage: Convergent plate boundaries also produce strong, deadly earthquakes. Earthquakes mark the motions of colliding plates and the locations where plates plunge into the mantle. These earthquakes can be shallow, intermediate or deep focus. Answer: the mantle
[EX A]:
Earthquakes mark the motions of colliding plates and the locations where plates plunge into what?