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.
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Question: Sentence1: harming an animal species has a negative impact on the population size of that species. 
Sentence2: the rarity of a species increases harm to population exponentially.

Answer: harming


Question: Sentence1: faulting of rock in Earth 's crust causes earthquakes. 
Sentence2: fault movement forms earthquakes.

Answer: earthquakes


Question: Sentence1: operating an automobile usually requires fossil fuels. 
Sentence2: Operating an automobile usually requires energy pollution from gasoline.

Answer:
automobile