The Great Lakes and the Corn Belt Region Became Known

The Great Lakes and the Corn Belt region became known as the "Rust Belt" because

A) Decades after the invention of the automobile,large numbers of auto scrapyards and recyclers appeared around manufacturing cities so the iron and steel could eventually be reused.
B) The large number of underground iron deposits that filtered into emerging underground springs gave the rocks of the region a yellowish-orange "rusty" tinge as it oxidized.
C) The region used to be the hub of the rail system developed during WWII to move goods across America,but as shipping goods by truck and airplane became more prevalent,the system decayed leaving an iron skeleton of its former glory.
D) The decay of the region's cities from deindustrialization,as steel mills and auto manufacturers moved to other parts of the world,and the resulting loss of population,increase in crime and chronic unemployment.