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: a planet rotating causes cycles of day and night on that planet. 
Fact 2: Rotation determines day and night, and the length of the day.

SOLUTION: a planet's rotation is what causes night.

PROBLEM: Fact 1: Communities consist of populations of different species. 
Fact 2: Biodiversity is a lot more than just the number of different plant and animal species.

SOLUTION: Communities consist of populations that are biodiverse.

PROBLEM: Fact 1: operating an automobile usually requires fossil fuels. 
Fact 2: Fossil fuels are not sustainable fuels.

SOLUTION:
Operating automobiles usually requires a fuel which is not sustainable.