Part 1. 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.
Part 2. Example
Sentence1: pesticides cause pollution. 
Sentence2: pollution can harm animals.
Answer: pollution.
Explanation: The word "pollution" is common to Sentence1 and Sentence2. So, it's a good answer.
Part 3. Exercise
Sentence1: Black Holes Black holes are the inevitable conclusion of Einstein's General Theory of Relativity. 
Sentence2: When a high-mass star collapses, it fulfills the inevitable conclusion Einstein's General Theory of relativity.
Answer:
Einstein's