The bending equation is written as

A

$$\frac {I}{M} = \frac {f}{y} = \frac {E}{R}$$

B

$$\frac {M}{I} = \frac {f^2}{y} = \frac {E^2}{R^2}$$

C

$$\frac {M}{I} = \frac {f}{y} = \frac {E}{R}$$

D

$$\frac {M^2}{I} = \frac {f^2}{y} = \frac {E^2}{R}$$