siddharthkapoor
The settlements in Colorado, whose year-round stable food resources and sedentary lifestyle permitted an increase in population,
was the foundation of the Mesoamerican civilization that followed a hundred years later.
A. was the foundation of the Mesoamerican civilization that followed
B. were at the foundation of the Mesoamerican civilization which followed
C. were the foundation of the Mesoamerican civilization that followed
D. were the foundation of the Mesoamerican civilization that had been following
E. was the foundation of the Mesoamerican civilization that follows
Split 1: The subject of sentence is "The settlements" - Plural. So all options that use singular "was" can be eliminated (options A and E are eliminated).
Split 2: Meaning.
The correct meaning is that the settlements WERE the foundation of Meso. civilization. Option B changes the intended meaning, since it uses "were at the foundation". Eliminate B
Finally, the Mesoamerican civilization FOLLOWED the settlements. Option D uses past perfect, which is incorrect. Eliminate D
That leaves us with option C, which is the correct option.