Read the excerpt from "Machu Picchu: A City in the Sky.” Machu Picchu was once an important place. It was a hidden retreat, or resting place, for an Incan emperor. His name was Pachacuti Inca Yupanqui. He ruled from 1438 to 1471. The city was built around 1450 CE. That was a time of war between the emperor and other Incan leaders. In this hidden city, he was safe from his enemies.

What is the central idea of the excerpt?

a)Machu Picchu, a hidden city, was built for an Incan emperor in the 1400s.
b)Pachacuti Inca Yupanqui, an Incan emperor in the 1400s, had many enemies.
c)Machu Picchu, a city in Peru, has been a hidden retreat for six hundred years.
d)Pachacuti Inca Yupanqui, fleeing his enemies, discovered an Incan retreat.