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: Rivers, rainwater, well water and most lakes contain fresh water. 
Sentence2: canyons are formed by rainwater.
[A]: rainwater


[Q]: Sentence1: First, the bottle is calibrated with a graduated cylinder. 
Sentence2: calibration is performed with a cylinder.
[A]: calibrated


[Q]: Sentence1: Behaviors that improve fitness increase through natural selection. 
Sentence2: behaviors that improve traits that relate to an animal's ability to survive and reproduce increases through natural selection.
[A]:
Behaviors