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: Common fossils include plant fossils like ferns.
[EX A]: plant

[EX Q]: Sentence1: protein is used to repair cells by the human body. 
Sentence2: Meat, fish and chicken are rich sources of protein.
[EX A]: protein

[EX Q]: Sentence1: Differentiation is the process by which unspecialized cells become specialized. 
Sentence2: Hair becomes specialized through differentiation.
[EX A]:
become