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

Q: Most of the gray matter is on the surface of the brain, surrounding white matter.

A: Most of the gray matter is on the surface of the brain, surrounding what other type of matter?
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Q: Insulin is made up of two polypeptide chains.

A: Insulin is made up of how many polypeptide chains?
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Q: The earliest animals were aquatic kind of invertebrates.

A:
The earliest animals were which kind of invertebrates?
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