Answer correctly for easy !

briefly explain one important connection between the economic systems of the north and the south in the period 1790 - 1840

D. The south produced cotton and the north used it to manufacture textiles.

Explanation:

Northern and Southern parts of US had many similarities and differences. These differences caused disagreements and eventually led to war. In the Northern US the economy was based on industry, it was dominated by factories and exported manufactured products, due to rocky soil and cold climate agriculture was not possible hence they didn't had to depend on the slave labour, most people worked in factories.  

The soil in south was based on agriculture as the soil was fertile and good for farming. Cotton, rice and tobacco was the main crops of the south. The farms and plantations were big and they needed thousands of workers to work on it. Due to huge labour need they had to either hire people to work or rely on the slave labour.

The cotton produced in the south was used in the north to manufacture textiles.