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: Sperm pass out of the body through the urethra. 
Sentence2: Sperm travel from the testicles through the vas deferens to the seminal vesicles and the prostate.

Answer: Sperm


Question: Sentence1: Water expands as it is heated, and glaciers melt. 
Sentence2: Boulders are formed by water expanding as it is heated.

Answer:
Water