How did inca develop their road system? a) they used mortar to hold the stones together.b) they built suspension bridges over rivers. c) they mixed copper and stone together to make the blocks.d) they laid roads in the cities, not in the less densely populated deserts.

The correct answer is D. They laid roads in the cities, not in the less densely populated deserts.

Explanation:

The Inca road system formed a network known as the royal highway. It facilitated the movement of armies, people, and goods and at the same time it provided an important physical symbol of imperial control. Across plains, deserts, and mountains, the network could connect settlements and administrative centers.

Many of these roads included bridges, causeways, stairways, and also some small stations as well as some luxurious complexes. Inca roads covered over 40,000 km, mainly in two main highways which run from north to south  across the Inca Empire.