Machu Picchu is considered to be a truly extraordinary archaeological  discovery and is one of South America's largest tourist sites. As many as one thousand visitors visit the ancient Incan  ruins daily. What draws vacationers and adventurers to this remote location high in the Andes Mountains of Peru ? A large part of the attraction is the mysteries that surround Machu Picchu. For example, Machu Picchu is considered "the lost city" of the Incas because it was never found by Spanish invaders and was known to only a few local peasants for almost four hundred years. The "city in the clouds", Machu Picchu's lasting beauty comes from the careful blending of its striking architecture with its mountaintop environment. Its greatest skill shows are in the stone structures, which equals that of the ancient Egyptians. The stone blocks were so appropriately cut that they fit together without the need for mud. The largest stones at Machu Picchu weigh as much as fifteen tons! It has been difficult to explain how the huge blocks were transported. The buildings, including many that have survived lots of earthquakes, contain stones which _ so perfectly that a knife cannot be forced between them. When compared to other ancient civilizations, it is difficult to understand how Machu Picchu could have been missed by the Spanish and lost from history for four hundred years. For many of the mysteries of Machu Picchu being unsolved, it is clear why Machu Picchu remains "the most famous ruins in all of South America". From the passage we can learn that   _  .
Machu Picchu has gone through lots of earthquakes all of the mysteries of Machu Picchu have been solved the city has never been discovered by people outside Machu Picchu is the most valuable ruins in history.
Question: Machu Picchu is considered to be a truly extraordinary archaeological  discovery and is one of South America's largest tourist sites. As many as one thousand visitors visit the ancient Incan  ruins daily. What draws vacationers and adventurers to this remote location high in the Andes Mountains of Peru ? A large part of the attraction is the mysteries that surround Machu Picchu. For example, Machu Picchu is considered "the lost city" of the Incas because it was never found by Spanish invaders and was known to only a few local peasants for almost four hundred years. The "city in the clouds", Machu Picchu's lasting beauty comes from the careful blending of its striking architecture with its mountaintop environment. Its greatest skill shows are in the stone structures, which equals that of the ancient Egyptians. The stone blocks were so appropriately cut that they fit together without the need for mud. The largest stones at Machu Picchu weigh as much as fifteen tons! It has been difficult to explain how the huge blocks were transported. The buildings, including many that have survived lots of earthquakes, contain stones which _ so perfectly that a knife cannot be forced between them. When compared to other ancient civilizations, it is difficult to understand how Machu Picchu could have been missed by the Spanish and lost from history for four hundred years. For many of the mysteries of Machu Picchu being unsolved, it is clear why Machu Picchu remains "the most famous ruins in all of South America". From the passage we can learn that   _  .
A. Machu Picchu has gone through lots of earthquakes
B. all of the mysteries of Machu Picchu have been solved
C. the city has never been discovered by people outside
D. Machu Picchu is the most valuable ruins in history.
Answer: