instruction:
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.
question:
Fact 1: Insects generally have two pairs of wings for flight. 
Fact 2: Flight enables many insects to move quickly away from predators.
answer:
insects generally have two pairs of wings to move quickly away from predators.


question:
Fact 1: volcanic ash in the atmosphere decreases the temperature by blocking the sun. 
Fact 2: Most volcanic ash consists of fine, dusty particles.
answer:
Fine, dusty particles erupted from volcanos decrease the temperature by blocking the sun.


question:
Fact 1: a cavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone. 
Fact 2: Limestone caves are formed when acids attack and dissolve the calcite in limestone.
answer:

caverns are formed from limestone.