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: Humans have collected and grown mushrooms for food for thousands of years. 
Fact 2: Foods rich in chlorine are mushrooms, parsley, sweet potato, rhubarb, and especially tomato.

SOLUTION: Humans have collected and grown foods rich in chlorine for thousands of years.

PROBLEM: Fact 1: Soil can be depleted of nutrients. 
Fact 2: For the nonrenewable resources, depletion means extraction of the available natural resources.

SOLUTION: soil nutrition can be extracted.

PROBLEM: Fact 1: an acid changes the color of litmus paper from blue to red. 
Fact 2: Acidity is traditionally measured with litmus paper which changes color at a certain acidity.

SOLUTION:
Acid changes the color of certain paper at different acidity.