The correct answers are B and D.
B) The Inca road system, known in Quechua language as Qhapaq Ñan, was the largest transportation system in Pre-Columbian South America. It connected important nodes of the Inca Empire following the Andes, from the North in what today is Colombia to the South in what today is Argentina.
D) They also built large stone cities in the Andes mountains, the most famous one among them was Machu Picchu, which is made completely out of giant blocks of stone fitted to each other without mortar.