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: a car engine usually converts gasoline into motion and heat through combustion. 
Fact 2: Combustion is never complete in gasoline and diesel engines.
answer:
Cars never completely convert gasoline into motion.


question:
Fact 1: Mammals can also generate little bursts of heat by shivering. 
Fact 2: All humans are mammals.
answer:
humans can generate little bursts of heat by shivering.


question:
Fact 1: melting means changing from a solid into a liquid by adding heat energy. 
Fact 2: Melting is a phase change.
answer:

A phase change changes a solid into a liquid using heat energy.