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: gills are used for breathing water by aquatic animals. 
Fact 2: Fish are backboned aquatic animals.

A: fish use gills for breathing water.
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Q: Fact 1: having food has a positive impact on an organism 's health. 
Fact 2: Animals eat plants for food.

A: Eating plants has a positive impact on the health of animals.
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Q: Fact 1: sound can be used for communication by animals. 
Fact 2: Sound Sound waves are mechanical waves.

A:
mechanical waves can be used for communication by animals.
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