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.

Q: Sentence1: creating wood-free paper does not require cutting down trees. 
Sentence2: creating printed media requires cutting down trees.

A: creating
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Q: Sentence1: an automobile engine transforms chemical energy into mechanical energy. 
Sentence2: cars transform chemical energy into mechanical energy.

A: chemical
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Q: Sentence1: Familiar things seen at greater distances are smaller than they appear close up. 
Sentence2: Optical tools are used for observing things that are smaller than they appear.

A:
appear
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