Between January and December 1991, while the U.S. economy was falling deeper into its recession, the interest rate on Treasury bills fell from 6.3 to 4.1 percent. Use the IS-LM model to explain this pattern of declining output and interest rates. Which curve must have shifted? Can you think of a reasonhistorically valid or simply imaginedthat this shift might have occurred? (hint: Showing the graph and the shift is a good idea!)