Fact 1: All life relies on a relatively narrow range of pH, or acidity.

Fact 2: All organisms have a life-span.

Given the two facts above, answer the question "Organisms rely on a relatively narrow range of what?" with the following options: 
- Decibels
 - water
 - food
 - relativity
 - acidity
 - spectrum
 - balance
 - Light


 

     acidity    