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: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Water freezes into ice when cooled.

Answer: freezes


Question: Sentence1: a battery converts chemical energy into electrical energy. 
Sentence2: Battery electricity comes conversion.

Answer: battery


Question: Sentence1: microbial fuel cells convert chemical energy into electrical energy. 
Sentence2: microbial fuel cells convert chemical energy into kinetic energy.

Answer:
cells