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: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.

Ex Output:
living


Ex Input:
Sentence1: when a hemisphere is tilted away from the sun , that hemisphere receives less direct sunlight. 
Sentence2: Sunlight is delivered in small packets of energy called photons.

Ex Output:
sunlight


Ex Input:
Sentence1: Steroids Steroids are lipids and, more specifically, derivatives of cholesterol. 
Sentence2: steroids are derivatives of cholesterol.

Ex Output:

cholesterol