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: Underground caves and caverns pose an exciting adventure to many. 
Sentence2: underground caves can be formed by carbonic acid in groundwater seeping through rock and dissolving limestone.

Underground