Bureaucrats "Go by the Book" Because

Bureaucrats "go by the book" because:

A) "The book" contains the laws and regulations it is their job to enforce.
B) Bureaucrats aren't that smart and can't think of other ways of doing things.
C) Bureaucrats only operate within their narrow field of specialization.
D) Bureaucrats can hide behind "the book" if their actions are unpopular.
E) Bureaucrats would get fired by the president if they didn't follow "the book".