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.

Q: Sentence1: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.

A: Smoking
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Q: Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: the emission of sulfur dioxide causes soil weathering.

A: causes
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Q: Sentence1: High pressure systems push air closer to the ground, preventing the formation of clouds. 
Sentence2: Clear weather occurs when air is pushed closer to the ground.

A:
ground
****