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: if an object is made of a material then that object has the properties of that material. 
Sentence2: If an object is made of a drug, then that object has the properties of that drug.

Answer: made


Question: Sentence1: gills are used for breathing water by aquatic animals. 
Sentence2: gills are used for breathing water by sharks.

Answer: are


Question: Sentence1: harming an animal species causes that animal 's population to decrease. 
Sentence2: Regular overfishing can decline an animal population to the point of extinction.

Answer:
decrease