Many Ions Do Not Have Tabulated Activity Coefficients nor Can

Many ions do not have tabulated activity coefficients nor can the activity coefficient be estimated,as the ion size is now known.The Davies equation is used to estimate the activity coefficient under these conditions.Which statement(s) is(are) NOT true for the Davies equation?
I The calculated activity coefficient is independent of the ion's size.
II The ion's charge,the solutions ionic strength and the ion size are required to calculate the activity coefficient.
III The Davies equation can be used up to ~ 0.5 M ionic strength.
IV The calculated activity coefficient is no more accurate than guessing the ion size to determine the activity coefficient.

A) II and IV
B) II
C) I
D) III and IV
E) III