Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Mouth Brooding. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding. If you look closely, you can see the eggs inside the mouth of the cardinalfish pictured here. Answer: mouth brooding

Answer: Some species of fish carry their fertilized eggs in their mouth until they hatch; this is called what?

Question: Passage: Light may transfer its energy to matter rather than being reflected or transmitted by matter. This is called absorption . When light is absorbed, the added energy increases the temperature of matter. If you get into a car that has been sitting in the sun all day, the seats and other parts of the car's interior may be almost too hot to touch, especially if they are black or very dark in color. That's because dark colors absorb most of the sunlight that strikes them. Answer: absorption

Answer: When light transfers its energy to objects, this is known as what?

Question: Passage: Rust is a combination of several different oxides of iron. The equations below show the steps involved in one of the many processes of rust formation. Answer: iron

Answer:
Rust consists of oxides of what element?