The correct response regarding an achievement of the U.S. government under the Articles of Confederation is:
It forced the Spanish to allow U.S. usage of the Port of New Orleans.
While the other options either refer to accomplishments that occurred after the Articles of Confederation (like the adoption of the U.S. Constitution) or do not accurately reflect the realities of the period (such as slavery being abolished under the Articles), the port usage issue was a key point of contention during that time, and diplomatic efforts were made regarding access to New Orleans.