How Did American Geographic Expansion and Economic Development Impact the South

How did American geographic expansion and economic development impact the South in 1850?

A) The South began to play a lesser role in national politics.
B) The South gained a veto-proof majority in Congress.
C) Southern cotton had the biggest influence on the national economy, resulting in the South having the highest real per capita income in the nation.
D) Geographic expansion and cotton's domination of the national economy led to the rapid extension of slavery in the territories won from Mexico in 1848.