Answer:
The purchase of bonds increases the amount of deposits in people's bank accounts, which enables banks to loan more money.
Step-by-step explanation:
When the Federal Reserve buys treasury bonds, it deposits money to the sellers' amounts. The current bondholder gives up the bond and gets money in exchange. The Federal Reserve becomes the new bondholder.
The action of buying treasury bonds increases money in individuals accounts and, consequently, an increase in deposits. An increase in deposits means the bank will have more money to lend out to firms and households. The banks will reduce interest rates to encourage borrowing, which increases the money supply in the economy.