The correct answer is C: All (a), (b), (c), and (d) are correct.

1–A: Satavahanas ruled the Deccan plateau from c. 1st century BCE to 3rd century CE, bridging northern and southern India through trade.

2–B: Pratishthana (modern Paithan, Maharashtra) was the Satavahana capital and a key political and cultural center.

3–C: Significant Indo-Roman trade during the Satavahana period led to discovery of Roman gold coins at archaeological sites in southern India.

4–D: Megasthenes served as Greek ambassador to Chandragupta Maurya's court at Pataliputra; his observations recorded in Indica are a key source for Mauryan history.