Fact 1: Astronauts require preserved food for extended flights.

Fact 2: For example, food contains Calories, units of energy content.

Given the two facts above, answer the question "What do astronauts require for long flights?" with the following options: 
- problems
 - nutrients
 - glycogen
 - danger
 - energy
 - sugar
 - hydration
 - trouble


 

     energy    