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: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Fossils are the remains of prehistoric life.
[EX A]: fossils

[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: Protozoa can be classified on the basis of how they move. 
Sentence2: Ciliates are ciliated protozoa.
[EX A]:
Protozoa