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: cutting down trees has a negative impact on an ecosystem. 
Fact 2: Ecosystems are living communities.

SOLUTION: Cutting down trees has a negative impact on living communities.

PROBLEM: Fact 1: Monotremes are mammals that reproduce by laying eggs. 
Fact 2: Like the platypus, an echidna is an egg laying mammal.

SOLUTION: Platypus are monotremes.

PROBLEM: Fact 1: chemical weathering causes iron in rock to oxidize. 
Fact 2: When iron oxidizes it produces iron oxide, more commonly referred to as rust.

SOLUTION:
Chemical weathering of iron in rock causes rust.