The first three North American, or classic, models were based on Chicago. What best explains this? A. Chicago was the first major city in the United States.
B. Chicago has been the most densely populated city since the census began.
C. Chicago is the only North American city that was planned in advance of being built.
D. Chicago is located on an isotropic plain and was able to expand to the north, south, and west without interruption caused by topography.