The main reason is that the North wasn't as agricultural so they didn't need slaves working the fields they where more mercantilist ( an economic system used to boost the nation's wealth using trade.)
The answer to your question is b
This example might illustrate the concept of interaction. This may mean that after the first meeting, they may again and learn more about each other, so the early impressions they formed will influence their feelings about each other in the future. His feelings towards her are influenced by how he knows her now.
