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.

Sentence1: Rivers, rainwater, well water and most lakes contain fresh water. 
Sentence2: canyons are formed by rainwater.
rainwater

Sentence1: Flowers produce seeds for reproduction. 
Sentence2: flowers require dispersal for reproduction.
Flowers

Sentence1: a planet rotating causes cycles of day and night on that planet. 
Sentence2: a planet's rotation is what causes night.

night