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: Consider Input: Sentence1: Populations Populations are subsets of a species. 
Sentence2: Gene flow occurs when individuals move into or out of a subset of a species.

Output: species


Input: Consider Input: Sentence1: Ribosomes are small organelles where proteins are made. 
Sentence2: Ribosomes are assembled inside the nucleus.

Output: Ribosomes


Input: Consider Input: Sentence1: Plants have a very clever way of using the energy from sunlight to make their food. 
Sentence2: Phytoplankton have a clever way of making food from sunlight energy.


Output: clever