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

Q: Phospholipids are the main component of the cell membrane.

A: What is the main makeup of the cell membrane?
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Q: Radioactivity is the release of particles and/or energy from the nucleus of an atom.

A: What is the release of particles and/or energy from the nucleus of an atom described as?
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Q: There are four valves in the heart.

A:
How many valves are in the heart?
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