Rank the following bonds in order from lowest credit risk to highest risk all with the same time to maturity, by their yield to maturity: (Rank: 1= lowest, 4 = highest)
Treasury bond with yield of 5.60 percent
United Airline bond with yield of 6.45 percent
Bank of America bond with a yield of 6.98 percent
Hewlett-Packard bond with yield of 9.27 percent