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.
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Question: Fact 1: energy is used for heating a building by a heating system. 
Fact 2: Energy used for heating is the single most commonly used form of energy worldwide.

Answer: Heating buildings is a very common production of energy worldwide.


Question: Fact 1: Mollusks live in most terrestrial, freshwater, and marine habitats. 
Fact 2: Clams, oysters and snails are familiar mollusks.

Answer: oysters live in most terrestrial, freshwater, and marine habitats.


Question: Fact 1: when a plant grows , the size of the leaves of that plant may increase. 
Fact 2: All oaks are plants.

Answer:
when an oak grows , the size of the leaves of that oak may increase.