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: a fire requires oxygen to burn. 
Sentence2: A fire requires something with exactly eight protons to burn.
[A]: burn


[Q]: Sentence1: Water erosion has similar consequences as wind erosion. 
Sentence2: exposure to water can cause erosion.
[A]: Water


[Q]: Sentence1: Hormones are chemical messengers that control many body functions. 
Sentence2: And like other downers, it slows bodily functions, including breathing and heart rate.
[A]:
body