instruction:
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: Viruses cause many human diseases. 
Fact 2: Some smallpox viruses are maintained in laboratories.
answer:
smallpox causes human disease.


question:
Fact 1: the volume of an object can be used to describe the size of that object. 
Fact 2: Size of waves depends on the mass and volume of the object that fell into the water.
answer:
The volume of an object depends on the mass of the object.


question:
Fact 1: sugar causes food to taste sweet. 
Fact 2: For example, the tongue determines the taste of foods, deciding whether a thing is sweet or bitter.
answer:

The tongue determines the flavor of sweet foods, like sugar.