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.

Ex Input:
Sentence1: a sifter is used for separating mixtures. 
Sentence2: a sifter is used for some recipes.

Ex Output:
sifter


Ex Input:
Sentence1: Organisms cluster around hydrothermal vents in the ocean floor. 
Sentence2: vents on the ocean floor are powered by heat.

Ex Output:
vents


Ex Input:
Sentence1: Carbon monoxide is a gas produced by furnaces and other devices that burn fuel. 
Sentence2: Carbon monoxide gas is an odorless and colorless gas that can kill.

Ex Output:

Carbon