Reserves equal deposits with the Fed plus vault cash
Option D
Explanation:
"Vault currency" simply is the cash a bank holds in buildings (most of which are normally kept in its caves) to satisfy everyday cash needs.
Foreign governments, the Bank, and perhaps most commercial banks in the USA are the primary providers of Federal Reservation Deposits. Federal Reserve Deposits may not be held by private citizens and businesses.
All FRD and FRN notices are reported as FRD liabilities. FRD liabilities, What the Fed have traded for (gold and mostly t-billion) these investments and notes are reported as the Fed's reserves.