Fact 1: Astronauts require preserved food for extended flights.

Fact 2: Freeze-drying Freeze drying is a method of preserving materials.

Given the two facts above, answer the question "Which of the following keeps food viable for extended flights? " with the following options: 
- evaporation
 - microwaving
 - boiling
 - freeze drying
 - layers of fat
 - deep frying
 - mechanical
 - Dehydration


 

    freeze drying     