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: Tree-ring dating the 1700 Cascadia earthquake. 
Sentence2: estimating the age of trees can be used in reviewing earthquake history.

A: earthquake
****
Q: Sentence1: Most water comes from precipitation. 
Sentence2: aquatic animals require precipitation to survive.

A: precipitation
****
Q: Sentence1: Electron transport is the final stage of aerobic respiration. 
Sentence2: That the cellular level, the final stage of breathing oxygen is electron transport.

A:
Electron
****