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: Earthquakes cause massive damage. 
Sentence2: tectonic plates being pushed together causes massive damage.

Answer: damage


Question: Sentence1: a fire requires oxygen to burn. 
Sentence2: Oxygen has  eight protons and eight electrons.

Answer: oxygen


Question: Sentence1: Evolution occurs by a process called natural selection. 
Sentence2: Speciation is an extension of evolution.

Answer:
Evolution