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.
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Question: Sentence1: People of all ages and activity levels perspire or sweat. 
Sentence2: Perspiration reduces body heat.

Answer: perspire


Question: Sentence1: protein is used to repair cells by the human body. 
Sentence2: Meat, fish and chicken are rich sources of protein.

Answer: protein


Question: Sentence1: knowledge of the stars can be used to navigate. 
Sentence2: Astronomy is the study of the planets, stars, and universe.

Answer:
stars