Unconvetional Monetary Policy

a) What are the unconventional monetary tools? Why do we need these unconventional tools?

b) According to Arvind Krisnamurthy and Annette Vissing-Jorgensen, what are the channels that make QEs effective in affecting the prices of purchases assets? in stimulating the real economy?

c) According to Arvind Krisnamurthy and Annette Vissing-Jorgensen, what is the order in which the Fed should unload the assets, accumulated from large-scale asset purchases program during and after the financial crisis of 2007-2009, in its balance sheet (treasuries, agency mortgage backed securities) when the economy recovers from the crisis? Why?