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.

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

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

Sentence1: Fossilization is the process that turns a once living thing into a fossil. 
Sentence2: Scientists who study  the process that preserves a once living thing are called paleontologists.

living