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

Q: What force increases a slide downhill and decreases a slide uphill?

A: gravity
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Q: How are electrons shared in covalent bonds?

A: equally
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Q: What are two other terms for dizygotic twins, which make good study subjects because they share many environmental conditions, but only about half of their polymorphisms?

A:
fraternal, non-identical
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