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: Veins generally carry deoxygenated blood. 
Fact 2: Blood carries blood cells.
Veins carry cells.

Fact 1: Specialization occurs when competing species evolve different adaptations. 
Fact 2: Instructional techniques are adapted to accommodate differences.
Specialization occurs when competing species evolve techniques to accomodate differences.

Fact 1: fossils are formed when layers of sediment cover the remains of organisms over time. 
Fact 2: Natural gas is a fossil fuel.

natural gas is formed from layers of sediment covering the remains of organisms over time.