The ancient Inca city of Macchu Picchu, perched on a ridge

Question

The ancient Inca city of Macchu Picchu, perched on a ridge in the Andes Mountains of Peru,  had been built at a high enough altitude that it often makes modern-day tourists from lower elevations sick with oxygen deprivation.  

 A) had been built at a high enough altitude that it often makes modern-day tourists from lower elevations sick with oxygen deprivation 
 B) had been built at so high of an altitude that it often makes modern-day tourists from lower elevations sick from oxygen deprivation 
 C) was built at a high enough altitude that modern day tourists from lower elevations often become sick with oxygen deprivation when visiting the city 
 D) was built at such a high altitude that modern-day tourists from lower elevations often become sick from oxygen deprivation when visiting the city 
 E) was built at so high of an altitude that it often makes modern-day tourists from lower elevations sick from oxygen deprivation

UMB · Answer

D.

It seems that there is no need to use Past perfect. Because there is no another past situation. A,B-out.
FROM>WITH so C-out.

"IT" in E doesn't have clear referent E-out

sludge · Answer

My reasoning exactly. Does the altitude make the tourist sick, or does the city? "It" is unclear.

iamba · Answer

OA is D

The ancient Inca city of Macchu Picchu, perched on a ridge

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