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 flashlight converts chemical energy into light energy. 
Sentence2: Only as long as there are batteries in the flashlight, the flashlight will function.
flashlight

Sentence1: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.
wind

Sentence1: Carbon may be stored in sedimentary rock for millions of years. 
Sentence2: Limestone is a type of sedimentary rock.

rock