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.

Fact 1: telephones are used for communication by two people by transmitting sound. 
Fact 2: All sounds are waves produced by the vibrations of material objects.
Telephones are used for communication by two people by transmitting waves produced by the vibrations of material objects.

Fact 1: chemical splashing can cause harm to humans. 
Fact 2: Humans are animals too.
chemical splashing can cause harm to animals.

Fact 1: mineral graphite is used for making pencil lead. 
Fact 2: Pencil lead is a mixture of graphite and clay.

Mineral graphite and clay are mixed together for a safe alternative to lead.