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.

Input: Consider Input: 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.

Output: calcium carbonate becomes a  reef.


Input: Consider Input: Fact 1: a warm front causes cloudy and rainy weather. 
Fact 2: If warm air is advancing on cold air, the front is designated a warm front.

Output: Warm air advancing on cold air can lead to cloudy and rainy weather.


Input: Consider Input: Fact 1: when metal conducts heat , that metal expands. 
Fact 2: Copper is a very ductile metal.


Output: When copper conducts heat it expands.