The correct answer is C) to secure control of the port of New Orleans.
A major reason for purchasing the Louisiana territory in 1803 was to secure control of the port of New Orleans.
With the purchase of the Louisiana territory, the United States could gain control of the port of New Orleans and could control the Mississippi River. With the revoke of the Spanis-U.S. treaty that authorized the U.S. to store goods in New Orleans, owned by the French, President Jefferson sent James Monroe to Paris, France, in order to help U.S. Minister France Robert Livingstone with the purchase of the Louisiana territory. Having purchased the Louisiana territory, the U.S. was able to secure control of the port of New Orleans and the Mississippi River.