Answer: Option 'c' is correct.
Step-by-step explanation:
The definition of the monetary base is that
monetary base is equal to the sum of currency, banks' reserves at the Federal Reserve and checkable deposits at banks.
It is not the sum of currency and banks' reserves at the Federal Reserve.
It is not currency and checkable deposits at banks.
It is not sum of U.S. government securities owned by the Federal Reserve.
Hence, Option 'c' is correct.