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: when metal conducts heat , that metal expands. 
Fact 2: Steel is a solution of metals.
answer:
when steel conducts heat, it expands.


question:
Fact 1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Fact 2: Coral is calcium carbonate with a trade of carotene.
answer:
calcium carbonate becomes a  reef.


question:
Fact 1: gravity causes objects that have mass to be pulled down on a planet. 
Fact 2: And roller coasters work with gravity.
answer:

Roller coaster work the same as any object having mass being pulled down on a planet.