TASK DEFINITION: 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.
PROBLEM: Fact 1: a laser is used for producing light. 
Fact 2: Lasers, for instance, produce coherent light.

SOLUTION: Lasers are used to produce a beam that is coherent.

PROBLEM: Fact 1: hearing is used for sensing sound by animals. 
Fact 2: All cats are animals.

SOLUTION: hearing is used for sensing sound by cats.

PROBLEM: Fact 1: All life relies on a relatively narrow range of pH, or acidity. 
Fact 2: Acids have low pH's.

SOLUTION:
All life relies on a relatively narrow range of low pHs.