Why is Spain, with three different law enforcement systems, considered centralized?

Select one:

a$.$ All three forces operate under the authority of the national government.

b$.$ All three forces report to local authorities.

c$.$ The Spanish Supreme Court has ultimate control of all three agencies since all police in Spain are members of the judicial police.

d$.$ All three forces are deployed from Madrid on the first of each month and serve one month duty at either the civilian, military, or local level.