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 gravitational pull of the Moon on Earth 's oceans causes the tides. 
Fact 2: The lower is the tide, the better is the wave.
answer:
gravitational pull of the moon causes waves.


question:
Fact 1: skin is used for protecting the body from harmful substances. 
Fact 2: Contamination is the unintended presence of harmful substances or microorganisms in food.
answer:
The skin is used for protecting the body from contamination.


question:
Fact 1: Courtship is behavior that is intended to attract a mate. 
Fact 2: Birds sing to defend territories and attract mates.
answer:

birds sing to defend territories and for courtship.