Answer:
D) purchases of both long-term Treasury securities and mortgage-backed securities.
Explanation:
Quantitative easing is basically a large scale purchase of securities carried out by the FED. When the FED purchases long term Treasury securities, or any other type of security including mortgage backed securities, it is increasing the economy's money supply. Since the economy was facing a very deep recession, by increasing the money supply the FED was trying to boost the economy and make it rebound.