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: weathering means breaking down rocks from larger whole into smaller pieces by weather. 
Fact 2: Massive boulders and tiny rocks influence the sound and path of water.
weathering means breaking down boulders by weather.

Fact 1: Lancelet larvae are free-swimming. 
Fact 2: Some types of snails are free swimming, while others are sessile.
lancelet larvae are not sessile.

Fact 1: eyes are used for seeing by animals by sensing light. 
Fact 2: Mammals are animals with a backbone.

Mammals use eyes to sense light.