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: rocks interacting with wind over long periods of time causes weathering. 
Fact 2: Rocks weather at different rates.

SOLUTION: wind affects rocks.

PROBLEM: Fact 1: acid rain has a negative impact on water quality. 
Fact 2: Acid rain is harmful rain.

SOLUTION: some rain is harmful.

PROBLEM: Fact 1: a radio is used for communication. 
Fact 2: Communication requires an idea, a message to share.

SOLUTION:
A radio is used to share an idea or message.