Answer:
The actions of the Fed in 2009 are consistent with an expansionary monetary policy and this policy reduces or keeps interest rates low.
When the Fed bought that many government securities, they flooded the economy with $300 billion in cash. This cash would make its way into the pockets of people and into their bank accounts as savings.
With that many savings, banks would have much more money to loan out to people and as a result of this increase in the supply of loanable funds, interest would fall in order to entice people to borrow more of these excess funds.