The office is a good one. If you haven’t ever watched it
<span>a representation in which each item corresponds to one or more bits of information, especially the information used to control the display of a computer screen.
</span><span>represent (an item) as a bitmap.
</span>
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!