The second alternative is correct (B).
The United States is a representative democracy.
The division between powers is one of the pillars of American democracy. In this context, each power has its attributions, among them, to supervise the actions of the other power.
Legislative power creates laws, but it also has the power to authorize some activities of executive power, including declaring war. Congressional authorization is required.
However, the legislative power indirectly represents the US people. In this way, the request for war is authorized by the representatives of the people.
