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: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.

Answer: living


Question: Sentence1: Animals behave in a variety of ways which enhance their chances of survival and reproduction. 
Sentence2: Animals learn to behave to increase chances of survival.

Answer: behave


Question: Sentence1: Experiments are often done in a lab. 
Sentence2: Trial runs are often done in labs.

Answer:
lab