Which of the following exemplifies a debate over "vertical" separation of powers under the U.S. Constitution's allocation of authority:

A. Questions about whether Congress or the President has the power to send the U.S. military into hostilities abroad.

B. A federal executive branch official refusing to testify before Congress on the grounds that her information is legally privileged.

C. An argument that a statute passed by Congress is unconstitutional because it regulates private conduct that does not substantially affect interstate commerce.

D. Arguments by Supreme Court Justices that Congress has no power to compel them to televise oral arguments.