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: Graphite and diamond are polymorphs of carbon. 
Sentence2: carbon polymorphs are used for making pencil lead.
carbon

Sentence1: Plants exhibit phototropism, or growing toward a light source. 
Sentence2: legumes grow towards a light source.

growing