the US central bank has stated goal of promoting sustainable economic growth, maintain a stable proce level, and promoting maximum employment. in order to acheive these goals the central bank has sveral tools at its disposal. which of the following is not one of the tools employed by the central bank?

1. change in reseve requirements.

2. change in the diacount rate

3. purchase and sale of S and P 500 stocks

4. purchase/ sale us government security such as treasury bonds.