Given a scientific question, generate a correct answer to it.

Q: When sparks from a steel grinder react with oxygen, what do they form?

A: iron oxide
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Q: On the ventral side of the embryonic disc, opposite the amnion, cells in the lower layer of the embryonic disk (the hypoblast) extend into the blastocyst cavity and form this?

A: yolk sac
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Q: What do we call coiled structures made of dna and proteins?

A:
chromosomes
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