Explanation:

The most important source for the study of Mauryan history is (D) Arthashastra. The Arthashastra, written by Kautilya (also known as Chanakya), is widely regarded as the most significant literary source for understanding the administration, politics, economy, and governance of the Mauryan Empire.

 It provides detailed information about the political and administrative systems of the time, making it invaluable for historians studying the period.