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: if soil is permeable then water easily flows through that soil.
Sentence2: if soil is permeable then h2o easily flows through the soil.

Ex Output:
flows

Ex Input:
Sentence1: All photos are digital images.
Sentence2: satellites are used to take photos from space.

Ex Output:
photos

Ex Input:
Sentence1: Ethanol, a form of alcohol, is already the most common biofuel.
Sentence2: a form of alcohol is used to produce electricity by burning.

Ex Output:
alcohol