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: the emission of sulfur dioxide causes acid rain. 
Sentence2: Sulfur dioxide emissions causes soil nutrients to be leached away.

Ex Output:
dioxide


Ex Input:
Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food cold is used to keep food simple and natural as possible.

Ex Output:
cold


Ex Input:
Sentence1: Neurons transmit nerve impulses to other cells. 
Sentence2: Neurons are the basic functional unit of the brain.

Ex Output:

Neurons