During the years from 1957 to 1976, the birth rate of the United States ______.

A．half of the population lived to the west of Appalachian Mountains
B．Americans had long been desirous of new territories
C．westward expansion was a solution to the conflicts between the two parties
D．America's industry was highly developed

A．slavery in the South was an evidence of American's racism
B．Indians were driven out of their homes into the west
C．Americans were threatened by wars during 1840s
D．Americans won their independence through westward expansion