Which agency apportions budget authority to the Department of Defense's comptroller?

The Office of Management and Budget (OMB) is responsible for overseeing the budgeting process for federal agencies, including the Department of Defense (DoD). Specifically, OMB allocates budget authority, which is essential for federal agencies to execute their programs and operations effectively. By setting priorities, the OMB ensures that available funds are distributed in alignment with the administration's policy objectives and legislative requirements.

The General Accounting Office (GAO), now known as the Government Accountability Office, provides auditing and accountability services but does not directly apportion budget authority. The Department of the Treasury manages federal finances but plays a different role in the budgeting process, focusing more on revenue management and financial reporting. The Congressional Budget Office (CBO) offers budgetary analyses and economic forecasts but does not allocate budget authority itself; rather, it assists Congress in understanding the implications of proposed fiscal policies. Thus, the OMB is the correct choice because it is directly involved in the apportionment of budget authority that supports the operations of the DoD.