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.

[EX Q]: Sentence1: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.
[EX A]: Smoking

[EX Q]: Sentence1: All chemical reactions require activation energy to get started. 
Sentence2: Catalysts lower the activation energy.
[EX A]: activation

[EX Q]: Sentence1: treating water is used to remove harmful substances before drinking. 
Sentence2: Water can be boiled to remove harmful substances before drinking.
[EX A]:
before