Though the City of Akron, Ohio Was Once King in the Tire

Though the city of Akron, Ohio was once king in the tire industry much of that has ceased to exist and the city is now trying to diversify and focus on polymers.This shows that

A) cities may shift their functions over time according to need.
B) all cities move gradually from more industrial pursuits to more service oriented ones.
C) most cities will always have a focus on automobile parts or production.
D) once the function of a city is set, it cannot change to some other function.