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: condensing causes a liquid to form. 
Sentence2: Air carries moisture that causes a liquid to form.

Answer: causes


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

Answer: seeing


Question: Sentence1: Mating is generally preceded by courtship. 
Sentence2: pigeons have a period of courtship.

Answer:
courtship