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: eyes are used for seeing by animals by sensing light. 
Fact 2: Light waves are electromagnetic waves.

Answer: eyes are used for seeing by animals by sensing electromagnetic waves.


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: Some parasites live on the surface of their host. 
Fact 2: Leeches are external parasites.

Answer:
Leeches are on the surface of the host .