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: 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: extreme heat and pressure change rock into metamorphic rock. 
Fact 2: Marble is a metamorphic rock.
answer:
extreme heat and pressure change rock into marble.


question:
Fact 1: Brain cells die quickly if their oxygen supply is cut off. 
Fact 2: Brain cells begin to die as soon as the heart stops pumping oxygen.
answer:

the heart stopping pumping can cut off oxygen to cells.