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: Runoff water is wasted water. 
Sentence2: Streams may start with wasted water.
wasted

Sentence1: an animal requires air for survival. 
Sentence2: It is breathed in by animals and restored to the air by the photosynthesis mechanism of plants.
air

Sentence1: Biodiversity generally increases from the poles to the equator. 
Sentence2: Ecosystem complexity generally increases from the poles to the equator.

equator