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: Infections of the lungs can be caused by bacteria, viruses or fungi. 
Sentence2: Pneumonia may be caused by viruses or injury.

viruses