Which financial ratios (list at least two) do you believe would be the most helpful to rate corporate bonds? Why?

Agencies such as Moody’s, Fitch, and Standard & Poor’s rate the default risk of various municipal and corporate bonds. While their rating systems are proprietary, it is widely known that they rely on financial ratios as key inputs to their bond ratings. Which financial ratios (list at least two) do you believe would be the most helpful to rate corporate bonds? Why?