What body is responsible for proposing amendments to the Constitution through a national convention?

The body responsible for proposing amendments to the Constitution through a national convention is indeed the states. Article V of the U.S. Constitution provides two methods for proposing amendments: one is through a two-thirds majority vote in both the House of Representatives and the Senate, and the other is through a national convention called by two-thirds of the state legislatures. This method emphasizes the role of states in the constitutional amendment process, allowing them to initiate changes directly if they believe it's necessary, reflecting the principle of federalism in the U.S. system of government.

The other options, while integral to the legislative and judicial processes, do not possess the authority to directly call for a national convention to propose amendments. The House of Representatives and the Senate can propose amendments but not through a national convention. The Supreme Court interprets the Constitution rather than proposes amendments, so these roles are distinctly separate in terms of constitutional authority and function.