Americans responded to the selective service act
a. with enthusiasm.
b. with antiwar riots.
c. by refusing to register.
d. by becoming conscientious objectors.

American responded to the selective service act : b. with antiwar riots
During antiwar riots, people showed their protest towards the selective service act  which tend to be led towards violent actions. Especially in the Youth age group of protesters

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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.