Fact 1: Cells cannot survive without oxygen.

Fact 2: Cells are the basic building blocks of life.

Given the two facts above, answer the question "what cannot surive without oxygen" with the following options: 
- basic building blocks of life
 - Microscopic organisms
 - an area swollen with pus
 - incapable of regurgitation
 - hydrogen
 - vacuum
 - outer space
 - the respiratory system


 

 basic building blocks of life        