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: protein is used to repair cells by the human body. 
Sentence2: Meat, fish and chicken are rich sources of protein.

A: protein
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Q: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: Friction causes the temperature of a toy to increase.

A: causes
****
Q: Sentence1: Plants are multicellular eukaryotes with cell walls made of cellulose. 
Sentence2: Water lillies are one of the most ancient angiosperm plants.

A:
Plants
****