The Mughal empire relied heavily on land revenue as its primary source of income. The land revenue system, notably during the reign of Akbar, was highly structured and involved detailed land measurement (called Zabt). While taxes were collected in kind and sometimes in cash, the key point is that revenue from agriculture formed the backbone of the empire's economy. This system helped fund the vast Mughal military, administration, and infrastructure.
Thus, the correct answer is (C) Revenue from the land was the economic mainstay of the empire.