How were the incan people able to build their empire in such challenging geography?

Each of the cultures that settled the area, however, learned to adapt to their environment. In doing so they made scientific advances. In the steep mountains, people made terraces for farming. On the coast, they developed irrigation systems so they could farm in the desert. As a result, farming could support large populations both on the coast and in the highlands, where they built cities a full two miles above sea level.

hope i helped

the answers is b.   environments.