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: Mammals conserve body heat with their hair or fur. 
Fact 2: Hair and feathers are both made of keratin.

SOLUTION: mammals conserve body heat with keratin.

PROBLEM: Fact 1: soil is formed by rocks eroding. 
Fact 2: Soils are formed by breakdown of rock.

SOLUTION: rocks eroding causes them to breakdown.

PROBLEM: Fact 1: air pollution can cause the pH of soil to decrease. 
Fact 2: Incineration releases pollutants into the air.

SOLUTION:
incineration can cause the pH of soil to decrease.