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: Light is necessary for photosynthesis, a process that produces oxygen. 
Sentence2: Darkness has a negative impact on the process that produces oxygen.

oxygen