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 causes that animal 's population to decrease. 
Sentence2: Wild animal populations have decreased drastically, due to both hunting and loss of habitat.

Answer: animal


Question: Sentence1: conserving water can be used for survival in a dry environment. 
Sentence2: conserving water can be used for survival in deserts.

Answer: conserving


Question: Sentence1: Copper is an essential mineral. 
Sentence2: copper is essential for the body.

Answer:
Copper