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: the type of material through which sound passes changes the speed at which sound travels. 
Fact 2: Sounds are made by vibrating objects.
The type of material through which a vibration passes changes the speed at which it travels.

Fact 1: the mass of a planet causes the pull of gravity on that planet. 
Fact 2: Well, weight is the force on a object caused by gravity trying to pull the object down.
The mass of a planet causes the weight of objects.

Fact 1: Viruses are not cells at all, so they are neither prokaryotes nor eukaryotes. 
Fact 2: Viruses Viruses are the smallest agents of disease.

The smallest agents of disease are not cells at all, so they are neither prokaryotes nor eukaryotes.