Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.

Q: Fact 1: hydropower requires damming a river. 
Fact 2: Hydropower is a renewable resource.

A: Damming a river can provide a renewable resource.
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Q: Fact 1: Energy is passed up a food chain or web from lower to higher trophic levels. 
Fact 2: Energy and carbon in organic compounds passed through food chain to herbivores and carnivores.

A: Carbon in organic compounds are passed through the food web from herbivores to carnivores.
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Q: Fact 1: increasing heat causes thermal expansion. 
Fact 2: Liquid propane is used to heat hot air balloons.

A:
liquid propane is used to expand hot air balloons.
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