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: Streams and rivers are crossed on rocks, beaver dams, on fallen trees or by wading. 
Sentence2: Hydropower requires beavers damming streams with fallen trees.

fallen