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: a wildfire changes an ecosystem drastically. 
Sentence2: Forest fires change an ecosystem drastically.
Example Output: changes

Example Input: Sentence1: mountains are formed by earthquakes. 
Sentence2: Mountains are formed by moving plates.
Example Output: are

Example Input: Sentence1: Some viruses have an envelope of phospholipids and proteins. 
Sentence2: Some viruses are also enclosed by phospholipids fat and molecules.
Example Output:
Some