Explanation:

Option (c) is correct: By the end of the ninth century, the Abbasid caliphate was in decline. Its place was taken by a series of states ruled by Islamized Turks. The Turks had entered the Abbasid empire during the ninth century as palace-guards and mercenary soldiers. Soon they emerged as the king-makers. As the power of the central government declined, provincial governors started assuming independent status, though for sometimes the fiction of unity was kept up by the caliph formally granting the title of amir-ul-umra (Commander of Commanders) on generals who were able to carve out a separate sphere of authority. These new rulers assumed the title of ‘amir’ at first, and of ‘sultan’ later on.