Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: The opening in the front of the eye is called pupil.

A: What is the opening in the front of the eye called?
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Q: The ability of matter to combine chemically with other substances is known as reactivity.

A: The ability of matter to combine chemically with other substances is known as?
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Q: Streams often start in mountains.

A:
Where do streams often start?
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