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: the volume of an object can be used to describe the size of that object. 
Fact 2: Size is a relative aggregate measure of volume and mass.

SOLUTION: The volume of an object can be used to measure the mass of the object.

PROBLEM: Fact 1: planting trees has a positive impact on an ecosystem. 
Fact 2: Biodiversity encourages a healthier ecosystem.

SOLUTION: planting trees has a positive impact on biodiversity.

PROBLEM: Fact 1: Oxygen is essential for cellular respiration for all aerobic organisms. 
Fact 2: Oxygen, for example, is produced by plants.

SOLUTION:
Plants are essential for cellular respiration for all aerobic organisms.