D. to ensure that Americans could use the Mississippi River and access the port of New Orleans
Explanation:
The main reason that President Thomas Jefferson sent representatives to France is to "ensure that Americans could use the Mississippi River and access the port of New Orleans."
Mississippi River and New Orleans port was essential to the United States trading routes, as it is the area in which they make export and import operations. Hence, Thomas Jefferson believed they need to control the area to be more successful in the importation and exploitation of the business, therefore the need to send a representative to France to make a deal on the Louisiana Purchase.
