Under the Confederation the federal government had virtually no say in what states did, but they did have a say in interactions between the states and foreign places. Therefore I would pick trade.
Under the Articles of Confederation, the power given to Congress was the power to make laws. To arrive at this answer, one can refer to the Articles of Confederation, which was the first constitution of the United States. The Articles specifically state the powers and limitations of the central government. By reading the text of the Articles, we can determine that Congress had the authority to make laws.
