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: Mollusks are invertebrates such as the common snail. 
Fact 2: Invertebrates have no backbone.
mollusks have no backbone.

Fact 1: Bioterrorism is another potential threat in the environment. 
Fact 2: Bioterrorism is a silent, but very real threat.
bioterrorism is silent.

Fact 1: chemical weathering causes iron in rock to oxidize. 
Fact 2: Limestone is a fairly common rock type.

chemical weathering causes iron in limestone to oxidize.