What is one function of the legislative branch?

The legislative branch is primarily responsible for making laws. While the options regarding making treaties and declaring war are typically associated with the powers of Congress, they are not functions of the legislative branch in their own right. Instead, these powers relate to the roles played by different branches of government through a system of checks and balances.

Making treaties is a power that involves negotiation and agreement with foreign nations, typically requiring approval from the Senate as part of the legislative process. Similarly, declaring war is a power granted to Congress, where they have the responsibility to make decisions regarding national military actions.

Therefore, the correct answer reflects the combination of these two powers that are significant responsibilities of the legislative branch, showing how legislative capabilities extend beyond just creating laws to influencing both domestic and foreign affairs significantly through treaties and war declarations. In this way, option D effectively recognizes the legislative branch's role in shaping the nation's policies and actions both at home and abroad.