TASK DEFINITION: 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.
PROBLEM: Fact 1: webbed feet are used for moving faster through water by aquatic animals. 
Fact 2: Ducks generally have webbing on their feet.

SOLUTION: Ducks can move fast through water.

PROBLEM: Fact 1: a breathing mask is used for keeping harmful particles from entering the respiratory system. 
Fact 2: When mold grows in the house, it can emit particles that travel through the air.

SOLUTION: A breathing mask can keep mold from entering the respiratory system.

PROBLEM: Fact 1: Fertilization occurs when a sperm and an egg fuse to form a diploid zygote. 
Fact 2: Penetration is when the sperm and egg meet and the sperm makes it way into the egg cytoplasm.

SOLUTION:
fertilization requires penetration.