Agencies such as Moody’s Fitch and Standard and Poors rate

Agencies such as Moody’s Fitch and Standard and Poors 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 2) do you believe would be the most helpful to rate corporate bonds? Why?