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: Neurons transmit nerve impulses to other cells. 
Fact 2: Nerves send electrical impulses to the muscles.

A: neurons transmit electricity.
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Q: Fact 1: the emission of sulfur dioxide causes acid rain. 
Fact 2: ACID RAIN Acid rain is polluted and harmful to the environment.

A: Sulfur dioxide emissions cause pollution and harm to the environment.
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Q: Fact 1: travelling requires navigation. 
Fact 2: For celestial navigation the navigator uses a sextant and a chronometer.

A:
Travelling requires a tool such as a sextant.
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