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: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.

Answer: cold


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: eating food that contains pesticides can have a negative impact on humans. 
Sentence2: eating food that contains DDT can have a negative impact on humans.

Answer:
can