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: All life relies on a relatively narrow range of pH, or acidity. 
Sentence2: humans rely on a relatively narrow range of acidity.

Output: acidity


Input: Consider Input: Sentence1: Leeches are external parasites. 
Sentence2: Leeches live on the surface of their hosts.

Output: Leeches


Input: Consider Input: Sentence1: using a car causes pollution. 
Sentence2: Air pollution Air pollution is a major threat to health.


Output: pollution