Explanation:

• The most important economic development of the Post Mauryan period was the thriving trade between India and the eastern Roman empire. In the beginning, a good deal of this trade was carried on by land,  but the movement of the Shakas, Parthians and Kushans beginning from the first century B.C. disrupted trade by land route.  Since the first century A.D. trade was carried on mainly by the sea.
• The Shaka and Kushan kingdoms used two routes from the north-western frontier to the western sea coast. Both these routes converged at Taxila, and were connected to the Silk Route passing through Central  Asia. The first route directly ran from the north to the south connecting Taxila with the lower Indus basin from where it passed on to Broach.
• The second route called Uttarapath was in more frequent use. From Taxila it passed through modern Punjab up to the western coast of Yamuna. Following the course of the Yamuna, it went southward to Mathura. From Mathura it passed on to Ujjain in Malwa and again from Ujjain to Broach on the western coast. Ujjain was the meeting point of another route which started from Kaushambi near Allahabad. Mahishmati lies on the Dakshinapath. Hence option (c) is the correct answer.