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: treating water is used to remove harmful substances before drinking. 
Fact 2: Chlorine is also used to treat water.
answer:
Chlorine is also used to remove harmful substances from water before drinking.


question:
Fact 1: natural magnetism is used for pointing north by a compass. 
Fact 2: Compasses point to the Magnetic Poles.
answer:
Natural magnetism is used to point to the magnetic poles.


question:
Fact 1: adding salt to a solid decreases the freezing point of that solid. 
Fact 2: Water sources can be frozen solid.
answer:

adding salt can lower water's freezing point.