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.

Fact 1: skin is used for protecting the body from harmful substances. 
Fact 2: Contamination is the unintended presence of harmful substances or microorganisms in food.
The skin is used for protecting the body from contamination.

Fact 1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Fact 2: Coral is calcium carbonate with a trade of carotene.
calcium carbonate becomes a  reef.

Fact 1: a light bulb is used for seeing in the dark. 
Fact 2: Electricity can be converted in to light using light bulbs, and even heat by using heating coils.

electricity is used to see in the dark.