What does it mean to capture an force others to serve in the military?

You want them to fight for your ideals and beliefs. You give them a choice between imprisonment or services under your army.  This will test the loyalties of captured troops whether they will remain loyal or not.  In the end the choice is theirs.

an informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.

the correct answer is d