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: volcanic ash in the atmosphere decreases the temperature by blocking the sun. 
Fact 2: Or a veil of tiny particles from a volcanic eruption can block the sun.
volcanoes can block the sun.

Fact 1: a fire requires oxygen to burn. 
Fact 2: There is no "gaseous" oxygen on the Moon and the Moon itself is bone dry.
A fire is cannot burn naturally above the surface of the Moon.

Fact 1: lungs are used for breathing air by land animals. 
Fact 2: Mammals are animals with lungs, and they breath air.

Mammals breathe with their lungs.