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: Human mating behavior also involves some competition. 
Sentence2: Human mating may lead to aggressive behaviors or displays of aggresion.
[EX A]: Human

[EX Q]: Sentence1: mineral graphite is used for making pencil lead. 
Sentence2: Diamond and graphite are made of carbon.
[EX A]: graphite

[EX Q]: Sentence1: Evolution occurs in response to a change in the environment. 
Sentence2: Different environments Life is a changing phenomenon.
[EX A]:
environment