What geographic factor enabled St. Louis, Missouri, to become a major urban center by the mid-1800s?
A.
Industries could use St. Louis' underground rivers to process goods without polluting the air.
B.
The city's location near the Mississippi and Missouri Rivers made it a good for trade.
C.
It was near enough to Cahokia for the settlers to trade easily with the Native Americans.
D.
At that time, St. Louis was located exactly in the middle of the United States' land.