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: Propane can be either a liquid or a gas. 
Sentence2: heat can be added to propane to change it's properties through the boiling process.

Output: Propane


Input: Consider Input: Sentence1: Plants exhibit phototropism, or growing toward a light source. 
Sentence2: Phototropism means growing toward the energy of light.

Output: phototropism


Input: Consider Input: Sentence1: Nephrons are the structural and functional units of the kidneys. 
Sentence2: Nephrons are the structural and functional units of the organ that filters blood.


Output: Nephrons