In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 

Q: Magma rises to the surface during a volcano. The magma undergoes changes in temperature. The magma undergoes changes in pressure. The magma cools. The magma solidifies. The magma crystallizes. Igneous rock is formed. 

A: How does igneous rock form?
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Q: Several types of gases form in the atmosphere. May come from different sources. The gases remain trapped in the atmosphere. Through the suns light the gases hold in heat and energy. Trap them in our atmosphere. The earth may become warmer this way. 

A: Describe the process of the greenhouse effect
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Q: Water comes into contact with something made of iron. The water combines with carbon dioxide in the air to form carbonic acid. As the acid is formed, the iron starts to dissolve. Some of the water breaks down into hydrogen and oxygen. The free oxygen and dissolved iron bond together. They form iron oxide, which is rust. 

A:
How does rust form?
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