Explanation:

Let’s break down those options so it’s clear why:

- Desired reserve ratio:

This is the percentage of deposits that banks are required (or want) to keep on hand, not lent out. It’s a policy or operational choice, not a sum of money in the economy.

- Excess reserves:

This is any money that commercial banks hold over and above the required reserves. It’s just a part of reserves, not the total currency plus total reserves.

- Monetary base:

Here’s the thing: monetary base, also called “high-powered money,” is exactly the sum of currency in people’s wallets and all the reserves (both required and excess) that commercial banks keep with the central bank. This is the foundation for all other forms of money in the economy.

- Money multiplier:

This is a number (not an amount of money) that shows how much the money supply increases based on the base — it’s about multiplication, not addition.

So yeah, the “monetary base” is the textbook answer here. If you picked that, you’ve nailed it.