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: using a gasoline engine requires burning gasoline. 
Fact 2: Gasoline and flammable liquid related burns, however, are a preventable problem.
answer:
using an engine requires burning flammable liquid.


question:
Fact 1: Light enters the eye through an opening called the pupil. 
Fact 2: Just behind the pupil is a lens.
answer:
light enters the eye through an opening just in front of the lens.


question:
Fact 1: Aging is associated with the death of cells. 
Fact 2: Cell death is natural.
answer:

aging is natural.