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.

Example Input: Sentence1: Autumn brings the changing of the seasons. 
Sentence2: Earth 's tilt on its rotating axis causes autumn.
Example Output: Autumn

Example Input: Sentence1: Viruses are parasites of cells. 
Sentence2: Populations of viruses do not grow through division because they are parasites.
Example Output: are

Example Input: Sentence1: operating an automobile usually requires fossil fuels. 
Sentence2: Fossil Fuels Fuels that are formed in the earth from plant or animal remains.
Example Output:
fossil