The correct answer is A. Kharaj.
Kharaj is a tax on land that was levied by the Muslim rulers on non-Muslims living in their empire. It was a form of poll tax that was paid in exchange for protection and security. The rate of kharaj varied depending on the type of land and the productivity of the land.
Jizya is a tax that was levied on non-Muslims who did not convert to Islam. It was a form of poll tax that was paid in exchange for the right to live and practice their religion in the Muslim empire. The rate of jizya was lower than the rate of kharaj.
Khums is a tax that is levied on the profits of trade and commerce. It is a form of wealth tax that is paid to the state. The rate of khums is 20%.
Zakat is a tax that is levied on the wealth of Muslims. It is a form of almsgiving that is paid to the poor and needy. The rate of zakat is 2.5%.
Kharaj was the most important source of revenue for the Muslim rulers during the Sultanate period. It was a major source of income for the state and it was used to finance the military, the bureaucracy, and other government expenses.