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: Metamorphic Rocks Metamorphic Rocks Metamorphic rocks are formed by pressure and heat. 
Sentence2: extreme heat and pressure form a type of rock.

formed