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: Fertilization occurs naturally in the fallopian tubes. 
Sentence2: fertilization is used for reproduction.

Answer: Fertilization


Question: Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: light is required for seeing.

Answer: seeing


Question: Sentence1: evaporation can be used for separating a solute from a solvent in a solution. 
Sentence2: Heating liquids can be used to separate a solute from a solvent in a solution.

Answer:
separating