In the late Ottoman period, modernization of diplomatic service was followed by the professionalization of ministry of foreign affairs. Before the 19th century, Reis-ül Küttap (Head of Secretaries) was mainly responsible for diplomatic correspondence. This body was established during the reign of Suleyman I and working subject to the Grand Vizier. The mission of Reis-ül Küttap in the state apparatus was to control duties of secretaries in the diplomatic correspondence. The correct answer is D.