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.
--------
Question: Fact 1: a compass is used to navigate oceans. 
Fact 2: Ocean waves travel on the surface of the water.

Answer: A compass is used to travel on the surface of the water.


Question: Fact 1: Chemical bonds form when substances react with one another. 
Fact 2: All substances are composed of molecules.

Answer: Chemical bonds form when molecules react with one another.


Question: Fact 1: Most ecosystems get energy from sunlight. 
Fact 2: Sunlight is turned into energy by plants.

Answer:
Most ecosystems need plants.