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: the Earth revolving around the Sun causes the seasons to change on its axis. 
Sentence2: Earth's orbital motion around the sun is key to the leaves of many trees changing colors.

Sun