Why is it important that congress have the power to regulate interstate commerce

How did most southern politicians of the 1860s feel about the issue of slavery? a) they supported slavery in current states, but were against its expansion into new states. b) they wanted to preserve slavery and supported its spread into new states. c) they wanted to prohibit the spread of slavery into new states and territories. d) they supported the emancipation of enslaved people in all states and new territories.