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: mineral graphite is used for making pencil lead. 
Sentence2: Diamond and graphite are made of carbon.
Example Output: graphite

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

Example Input: Sentence1: Producers use energy and inorganic molecules to make food. 
Sentence2: green plants use energy and inorganic molecules to make food.
Example Output:
energy