Concept:Selling treasury bills is a monetary policy tool used by the central bank to control the money supply in the economy.Explanation:When the central bank sells treasury bills to the public, buyers pay with cash from their bank accounts.This action withdraws money from the banking system and reduces the amount of cash in circulation.The main purpose is to mop up excess liquidity when there is too much money in the economy.This helps to control inflation and stabilize the economy.Answer:D. reduce cash in circulation