What was the economic system in South in the mid-1800s?

There was great wealth in the South, but it was primarily tied up in the slave economy. In 1860, the economic value of slaves in the United States exceeded the invested value of all of the nation's railroads, factories, and banks combined.

Explanation:

Correct

A.Humans first began planting crops during the Neolithic Revolution. In addition, they also began domesticating animals.

I've underlined the transition words in that sentence -- "in addition."  Words such as in addition, also, or likewise show a relationship of similarity to preceding material in the previous sentence.  Transition words like but, rather, or, and however show a relationship of difference to what was stated in a prior sentence or paragraph. There are also transitional phrases that effects or consequences, like as a result  or in consequence.  There are transitional words/phrases that point to examples or support of a point: for instance, namely, as an illustration, etc.    And there are transition words that set up a conclusion: as has been shown, in summary, etc.