Why are archaeologists interested in the cave paintings found near lascaux in southern france?
the paintings are the first evidence of early humans ever found in france.
the caves did not exist during the last ice age.
the paintings provide evidence that humans had become more complex.
the cave paintings are worth a great deal of money.

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.