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: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: the mass of a planet is what causes things to have weight.

Answer: mass


Question: Sentence1: measuring the hardness of minerals requires scratching those materials. 
Sentence2: To figure out the hardness of a mineral, the Moh's scale of hardness is used.

Answer: minerals


Question: Sentence1: Testosterone stimulates the reproductive organs to develop into male organs. 
Sentence2: Testosterone stimulates the reproductive organ to form male genitalia.

Answer:
Testosterone