The correct answer is the letter B. So the phrase stands: During the 1800s, the north built more factories, while the south remained agricultural and traditional.
Here is a brief explanation:
One of the causes that motivated the secession war was that while in the North the cold climate and rocky soil created a trend towards trade, manufacturing and regional development in the South, the hot climate and fertile soil favored agriculture, developed under the Plantation system (large monoculture properties with slave labor and production directed to the foreign market), favoring a rural and aristocratic lifestyle.
In addition, while the Northern region became more and more industrialized, the South became more and more agricultural. Inevitably, this led to the collision of the interests of the two regions, represented by the Union's protectionist and abolitionist economic policy and that liberalism practiced by the slaveowners and confederate aristocrats.