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: Batteries are a better source of DC electricity. 
Sentence2: a flashlight requires batteries to produce light.
Batteries

Sentence1: erosion of soil has a negative impact on the environment. 
Sentence2: erosion of soil has a negative impact on forests.
erosion

Sentence1: Another source of energy is hydropower. 
Sentence2: damming a river is a source of energy.

energy