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: All life relies on a relatively narrow range of pH, or acidity. 
Sentence2: humans rely on a relatively narrow range of acidity.
acidity

Sentence1: Aquatic animals are adapted to living within certain salinity ranges. 
Sentence2: Animals adapted to living within certain salinity ranges require great amounts of water to survive.
adapted

Sentence1: For adolescents, ages 12-18. 
Sentence2: Ages 12-18 is a time of significant mental, emotional, and social changes.

12-18