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.
--------
Question: Sentence1: protein is used to repair cells by the human body. 
Sentence2: Meat, fish and chicken are rich sources of protein.

Answer: protein


Question: Sentence1: Cancer is a disease in which cells divide out of control. 
Sentence2: Cancer is a disease in which cells grow and divide rapidly.

Answer: Cancer


Question: Sentence1: gases from burning coal and oil dissolving in water in the atmosphere causes acid rain. 
Sentence2: gases from burning coal and oil dissolving in water in the atmosphere is harmful.

Answer:
atmosphere