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: Chemical energy converted to light energy requires batteries.
chemical

Sentence1: Very often their only metal object in the house is a cooking pot or a knife. 
Sentence2: sharpening a knife causes it to change shape.
knife

Sentence1: An ecosystem includes the organisms and their habitat. 
Sentence2: energy enters organisms and their habitat in the form of sunlight or chemical compounds.

habitat