Answer:
Open Market operation is the most used instrument for controlling week to week changes in the money supply.
Explanation: An open market operation is an activity by the central bank to give or take it's currency to or from a bank or a group of banks.The goal of open market operation is to supply liquidity to the commercial bank and sometimes to take surplus liquidity from the commercial bank in order to manipulate the short term interest and the supply of base money to a economy. So open market operation is the best way to control the week to week changes of money supply.