Definition: 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: Sentence1: a breathing mask is used for keeping harmful particles from entering the respiratory system. 
Sentence2: a breathing mask is used for keeping harmful particles from entering the lungs.

keeping