Why do scientists perform multiple trials of the same experiment?

It would be D because they do that because they want to make sure that the other scientist's answer or results are correct

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.