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 type of material through which sound passes changes the speed at which sound travels. 
Sentence2: the type of material through which mechanical waves pass change the speed at which they travel.

through