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.
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Question: Fact 1: most canyons are formed by flowing rivers through erosion over long periods of time. 
Fact 2: Erosion was monitored by means of erosion pins.

Answer: Canyon changes are tracked with pins.


Question: Fact 1: Carbon may be stored in sedimentary rock for millions of years. 
Fact 2: Sedimentary Rocks One of the commonest sedimentary rocks is sandstone.

Answer: Carbon may be stored in sandstone for millions of years.


Question: Fact 1: operating an automobile usually requires fossil fuels. 
Fact 2: Fossil fuels are a finite resource.

Answer:
Automobiles  usually require a finite resource.