When you talk about how two things are different, you are: reviewing
comparing
contrasting
describing

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.

answer; the intervening variable;

answer; you are making a normative argument and i am making a positive argument;

answereruption of molten material; magnetic stripes in the rock of the ocean floor; the age of the rocks themselves;