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.

Input: Consider Input: Fact 1: Light enters the eye through an opening called the pupil. 
Fact 2: Light is essential to vision.

Output: vision requires the pupil.


Input: Consider Input: Fact 1: cutting down trees has a negative impact on an ecosystem. 
Fact 2: An ecosystem can be in a desert, a tropical jungle, an ocean or a pond.

Output: cutting down trees has a negative impact on a jungle.


Input: Consider Input: Fact 1: Brain cells die quickly if their oxygen supply is cut off. 
Fact 2: If the oxygen supply to the brain is cut off, a stroke can occur.


Output: Brain cells die quickly if a stroke occurs.