The computer-generated simulation of a three-dimensional image or environment that can be interacted with in a seemingly real or physical way by a person using special electronic equipment, such as a helmet with a screen inside or gloves fitted with sensors.
Answer:
A Document is a virtual paper that you can type on
Explanation:
A piece of written or electronic paper that provides information or evidence or that serves as an record.
Hello there!
They already gave you the answer just by saying "while serving his or her nation". So, the only way you can serve your nation is when you join the military.
So, the correct missing word is Joining the military.
I hope this helps!