Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

[Q]: Sentence1: All oaks are trees. 
Sentence2: Cutting down oaks has a negative impact on an ecosystem.
[A]: oaks


[Q]: Sentence1: Populations Populations are subsets of a species. 
Sentence2: Gene flow occurs when individuals move into or out of a subset of a species.
[A]: species


[Q]: Sentence1: Aging occurs as cells lose their ability to divide. 
Sentence2: cells can be damaged when they lose their ability to divide.
[A]:
ability