Fact 1: Astronauts require preserved food for extended flights.

Fact 2: Preservatives are added to extend the shelf life.

Given the two facts above, answer the question "What prolongs the storage life of food in space?" with the following options: 
- hydrogen and oxygen
 - preservatives
 - Dehydration
 - heating liquids
 - Fuel cells
 - heat energy
 - hard outer covering
 - layers of fat


 

  preservatives       