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 $4\mathrm{.}65$ percent

United Airline bond with yield of $9\mathrm{.}07$ percent

Bank of America bond with a yield of $6\mathrm{.}25$ percent

Hewlett$-$Packard bond with yield of $6\mathrm{.}78$ percent