Definition: 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.
Input: Sentence1: Fossil fuels are coal, oil, and natural gas. 
Sentence2: gases released during the use of coal, oil, and natural gas causes global warming.

natural