Did the financial crisis of 2007-2009 affect financial and nonfinancial firms to the same extent? For the period beginning in 2006, plot the spread between the interest rates on three-month non-financial commercial paper (FRED code: CPN3M) and three-month Treasury bills (FRED code: TB3MS). Plot a similar spread using the interest rates on three-month financial commercial paper (FRED code: CPF3M) and Treasury bills (FRED code: TB3MS). Compare the evolution of these two spreads.