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.

[EX Q]: Sentence1: Speciation events are thus examples of macroevolution. 
Sentence2: Speciation events occur over geologic time above the level of the species.
[EX A]: Speciation

[EX Q]: Sentence1: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.
[EX A]: bike

[EX Q]: Sentence1: intense heat has a negative impact on an organism. 
Sentence2: fire has a negative impact on most organisms.
[EX A]:
impact