The correct answer is C) hierarchical authority.
The principle of bureaucracy that the quotation demonstrates is the hierarchical authority.
This principle states that when the leader has more authority when he occupies the highest place in the Organization. This leader at the top of the hierarchy is entitled to make the most difficult of the decisions. In this case, that is why President Obama commented that the most difficult decisions had to be made by him. Other kinds of decisions could have been made by other members of his cabinet.