What makes the housing, ceremonial structures, and irrigation works of the Anasazi people in the American Southwest exceptional?

a) They were built without using beasts of burden, the wheel, metal, or a written language.
b) They were decorated with elaborate, abstract, geometric shapes and patterns.
c) They resemble structures built by Neolithic cultures in the Middle East.
d) Their ruins have survived thousands of years despite extreme climate changes.

Answer: A