Answer:
D. He created the Royal Road
Step-by-step explanation:
King Darius known as Darius the great was the 3rd kind of the Achaemenid empire. He reigned for a period of 36years. He conquered lands and also improved various economic systems.
Darius improved the persian empire by creating the royal road.
This road gave the Persian officials the ability to reach the cities they conquered all through the empire.