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: air pollution can cause the pH of soil to decrease. 
Fact 2: Acidity is measured with a pH meter or with pH paper strips.
answer:
air pollution can cause the Acidity of soil to decrease.


question:
Fact 1: bacteria in soil convert atmospheric nitrogen into a form usable by plants. 
Fact 2: Plants have to have nitrogen to grow.
answer:
bacteria helps plants grow.


question:
Fact 1: magnetism can cause objects to repel each other. 
Fact 2: Electrical currents cause magnetic fields.
answer:

Electrical currents can cause objects to repel each other.