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 a cooler object touches a warmer object , thermal conduction occurs. 
Fact 2: Thermal conductivity varies with sediment type.
answer:
When a cooler object touches a warmer object, conductivity varies with sediment type.


question:
Fact 1: the surface of a beach is formed by mechanical weathering. 
Fact 2: Most beaches are of white coral sand.
answer:
Coral is turned to sand by mechanical weathering.


question:
Fact 1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Fact 2: An insect has a hard outer covering called an exoskeleton.
answer:

Many corals secrete a hard outer covering that builds up to become a coral reef.