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

Q: Zero is the net force acting on an object when two equal forces are applied from opposite directions.

A: What is the net force acting on an object when two equal forces are applied from opposite directions?
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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: Differences between organisms reflect differences between their nucleotide sequences rather than between their genetic codes.

A:
Differences between organisms reflect differences between their nucleotide sequences rather than between their what?
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