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: high pressure systems cause clear weather. 
Sentence2: Weather Clear weather usually means good visibility.

Answer: clear


Question: Sentence1: All chemical reactions require activation energy to get started. 
Sentence2: Catalysts lower the activation energy.

Answer: activation


Question: Sentence1: detailed observation of celestial objects requires a telescope. 
Sentence2: Detailed observation of celestial objects requires the collecting of light and magnifying it.

Answer:
celestial