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

[EX Q]: Sentence1: Sound vibrations can be compared to pond ripples. 
Sentence2: dropping an object into water causes pond ripples.
[EX A]: pond

[EX Q]: Sentence1: most canyons are formed by flowing rivers through erosion over long periods of time. 
Sentence2: Rivers, rainwater, well water and most lakes contain fresh water.
[EX A]:
rivers